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| {{Redirect|hp|the technology corporation|Hewlett-Packard|other uses|HP (disambiguation)}}
| | What's next? I've experienced marketing for several years, over again. Every new strategy I observe causes me to laugh at the start and just when I believe I've seen it all, I get shocked all. But then results can be found in the image. You can consider it. I'm discussing Pixel Ads.<br><br> |
| {{Two other uses||The Chemical Brothers song|Horse Power (song)|the machine also known as a "horse power"|Horse engine}}
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| '''Horsepower''' ('''hp''') is the name of several [[units of measurement]] of [[power (physics)|power]], the rate at which [[work (physics)|work]] is done. The most common conversion factor, especially for electrical power, is 1 hp = 746 [[watt]]s. The term was adopted in the late 18th century by [[Scottish people|Scottish]] engineer [[James Watt]] to compare the output of [[steam engine]]s with the power of [[draft horse]]s. It was later expanded to include the output power of other types of [[piston engines]], as well as [[turbine]]s, [[electric motor]]s and other machinery.<ref>[http://www.britannica.com/EBchecked/topic/272384/horsepower "Horsepower"], ''Encyclopedia Britannica Online''. Retrieved 2012-06-24.</ref><ref>[http://www.britannica.com/EBchecked/topic/291305/International-System-of-Units-SI "International System of Units" (SI)], ''Encyclopedia Britannica Online''. Retrieved 2012-06-24.</ref> The definition of the unit varied between geographical regions. Most countries now use the [[International System of Units|SI]] unit ''[[watt]]'' for measurement of power. With the implementation of the EU Directive [[Units of Measure Directive#Directive 80/181/EEC|80/181/EEC]] on January 1, 2010, the use of horsepower in the EU is only permitted as supplementary unit.{{Citation needed|date=June 2012}}
| | <br><br>Applications like google adsense let you generate by either ticks or page-thoughts. Ticks reference the clicks of the visitor of one's site for the ads you've placed. The percentage of clicks per perception is dependent upon the click-through-rate or CTR. You're paid per click to the advertisements in your corner. The amount varies depends on plenty of specifics. Meaning it is never constant.<br><br>There are mailing mail and support corporations which have their very own bulk mail permit and could deal your parts for you. Try Looking In your neighborhood yellow pages under "mailing or shipping services." See below for more information on mass mailing companies.<br><br>I do benefit from the Enzyte commercials. In these penile enhancement commercials the men that have the perpetual smiles are the ones that have applied the products (their wives are grinning as well). Every commercial features a really pristine, whitecollar, 1950s approach close to landscape and clothing.<br><br>I do not know about you, but it left me scratching my head and wondering just what Arby's was thinking if they set this commercial out there for us all to see. It did not keep me attempting to rush to my nearest restaurant to experience the sub these were selling. Rather, it left me feeling ashamed.<br><br>This is another frequent cost effective [http://www.advertisingservicesguide.com/ Advertising Agencies] proven fact that you are able to certainly benefit from. Printing a few posters of the business and whether or not it's costeffective, a few standees too. Put these up at-all the areas which may get you company. As an example, easily opened up a fresh DVD rental showroom, I would put these up at auditoriums, cinemas and external college grounds. I am getting the crowd that is most ideal for my company, as a result. Similarly, if I opened up a storage, I'd put these up external restaurants and offices and at gasoline stations too. You can submit advertisements in magazines that participate in the exact same niche as your business after examining the price-performance.<br><br>(2) Create (or re-write) yours to make use of reliable direct-response advertising techniques (statements, sub-heads, chatting with them feel (not at them), robust close, impressive offer, time limited, and ask for motion).<br><br>Number capabilities. McDonald's Big Mac had "two all-beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame seed bun?" Nyquil has applied the exact same approach. |
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| ==Definitions of term==
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| Units called "horsepower" have differing definitions:
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| * The ''mechanical horsepower'', also known as ''imperial horsepower'', of exactly 550 [[Foot-pound (energy)|foot-pounds]] per second is approximately equivalent to 745.7 watts.
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| * The ''metric horsepower'' of 75 [[Kilogram-force|kgf]]-m per second is approximately equivalent to 735.5 watts.
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| **The ''Pferdestärke'' PS (German translation of horsepower) is a name for a group of similar power measurements used in Germany around the end of the 19th century, all of about one metric horsepower in size.<ref>[http://www.sizes.com/units/horsepower.htm "Horsepower"], ''Sizes.com''. Retrieved 2009-02-05</ref><ref>[http://www.sizes.com/units/horsepower_metric.htm "Metric Horsepower"], ''Sizes.com''. Retrieved 2012-06-24.</ref><ref>"Conversion Factors", page F-313 of ''Handbook of Chemistry and Physics'', 58th Edition, CRC Press Inc., Cleveland, Ohio ISBN 0-8493-0458-X, 1977, Robert C. Weast (ed.)</ref>
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| * The ''boiler horsepower'' is used for rating steam [[boiler]]s and is equivalent to 34.5 pounds of water evaporated per hour at 212 degrees [[Fahrenheit]], or 9,809.5 watts.
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| * One horsepower for rating [[electric motor]]s is equal to 746 watts.
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| * Continental European electric motors used to have dual ratings, using a conversion rate of 0.735 kW for 1 hp
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| * British [[Royal Automobile Club]] (RAC) horsepower is one of the [[tax horsepower]] systems adopted around Europe which make an estimate based on several engine dimensions.
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| ==History of the unit==
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| The development of the [[steam engine]] provided a reason to compare the output of [[horse]]s with that of the engines that could replace them. In 1702, [[Thomas Savery]] wrote in [[The Miner's Friend]]:<ref>[http://www.history.rochester.edu/steam/savery/ Rochester history department website: "The miner's friend"] Accessed July 21, 2011</ref> "So that an engine which will raise as much water as two horses, working together at one time in such a work, can do, and for which there must be constantly kept ten or twelve horses for doing the same. Then I say, such an engine may be made large enough to do the work required in employing eight, ten, fifteen, or twenty horses to be constantly maintained and kept for doing such a work…" The idea was later used by [[James Watt (inventor)|James Watt]] to help market his improved [[steam engine]]. He had previously agreed to take royalties of one third of the savings in coal from the older [[Newcomen steam engine]]s.<ref>{{Cite web |url= http://www.pballew.net/arithm17.html#hp |title=Math Words — horsepower |publisher= pballew.net |accessdate=2007-08-11 |postscript= }}</ref> This royalty scheme did not work with customers who did not have existing steam engines but used horses instead. Watt determined that a horse could turn a [[Horse mill|mill wheel]] 144 times in an hour (or 2.4 times a minute). The wheel was 12 feet in radius; therefore, the horse travelled 2.4 × 2π × 12 feet in one minute. Watt judged that the horse could pull with a [[force]] of 180 pounds. So:
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| :<math> P = \frac{W}{t} = \frac{Fd}{t} = \frac{(180 \text{ lbf})(2.4 \times 2 \pi \times 12 \text{ ft})}{1 \text{ min}} = 32,572 \ \frac{\text{ft} \cdot \text{lbf}}{\text{min}}.</math>
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| This was rounded to an even 33,000 ft·lbf/min.<ref>{{Cite journal|last=Tully |first=Jim |publisher=American Society of Mechanical Engineers |title=Philadelphia Chapter Newsletter |date = September 2002|url=http://sections.asme.org/Philadelphia/sept02.htm |accessdate=2007-08-11|postscript=}}</ref>
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| Others{{Who|date=November 2009}} recount that Watt determined that a pony could lift an average {{convert|220|lbf|kN|abbr=on}} {{convert|100|ft|m|abbr=on}} per minute over a four-hour working shift. Watt then judged a horse was 50% more powerful than a pony and thus arrived at the 33,000 ft·lbf/min figure.<ref>{{cite web|last=Marshall|first=Brian|title=How Horsepower Works|url=http://www.howstuffworks.com/horsepower.htm|accessdate=27 June 2012}}</ref>{{Better source|date=November 2013}} ''Engineering in History'' recounts that [[John Smeaton]] initially estimated that a horse could produce 22,916 foot-pounds per minute. [[John Theophilus Desaguliers|John Desaguliers]] had previously suggested 44,000 foot-pounds per minute and Tredgold 27,500 foot-pounds per minute. "Watt found by experiment in 1782 that a '[[draft horses|brewery horse]]' could produce 32,400 foot-pounds per minute." James Watt and Matthew Boulton standardized that figure at 33,000 the next year.<ref>{{Cite journal |url=http://print.google.com/print?id=AVn_Sm56OCoC&pg=171&lpg=171&dq=smeaton&sig=6N_TJXrLqwQI-Fm7mU9ebKS1djA |title=Engineering in History |first= Richard Shelton |last= Kirby |publisher=Dover Publications |page=171 |date= August 1, 1990 |isbn=0-486-26412-2 |accessdate=2007-08-11 |postscript=}}</ref>
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| Most observers familiar with horses and their capabilities estimate that Watt was either a bit optimistic or intended to underpromise and overdeliver; few horses can maintain that effort for long. Regardless, comparison with a horse proved to be an enduring marketing tool.
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| In 1993, R. D. Stevenson and R. J. Wassersug published an article calculating the upper limit to an animal's power output.<ref>{{Cite journal |last=Stevenson |first=R. D. |last2=Wassersug |first2=R. J. |year=1993 |title=Horsepower from a horse |journal=[[Nature (journal)|Nature]] |volume=364 |issue=6434 |page=195 |doi=10.1038/364195a0 }}</ref> The peak power over a few seconds has been measured to be as high as 14.9 hp. However, Stevenson and Wassersug observe that for sustained activity, a work rate of about 1 hp per horse is consistent with agricultural advice from both 19th and 20th century sources.
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| When considering [[human-powered equipment]], a healthy human can produce about 1.2 hp briefly (see [[orders of magnitude (power)|orders of magnitude]]) and sustain about 0.1 hp indefinitely; trained athletes can manage up to about 2.5 hp briefly<ref>Eugene A. Avallone et. al, (ed), ''Marks' Standard Handbook for Mechanical Engineers 11th Edition '', Mc-Graw Hill, New York 2007 ISBN 0-07-142867-4 page 9-4</ref>
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| and 0.3 hp for a period of several hours.
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| ==Calculating power==
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| If [[torque]] and [[angular speed]] are known, the power may be calculated. The relationship when using a coherent system of units (such as [[SI]]) is simply
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| :<math>P = \tau \omega</math>
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| where <math>P</math> is power, <math>\tau</math> is torque, and <math>\omega</math> is angular speed. But when using other units or if the speed is in revolutions per unit time rather than radians, a conversion factor has to be included. When torque is in [[pound-foot (torque)|pound-foot]] units, [[rotational speed]] <math>(f)</math> is in [[rpm]] and power is required in horsepower:
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| :<math>P \text{(hp)} = {\tau \text{(ft} {\cdot} \text{lbf)} \times f \text{(rpm)} \over 5252}</math>
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| The constant 5252 is the rounded value of (33,000 ft·lbf/min)/(2π rad/rev). | |
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| When torque is in inch pounds:
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| :<math>P \text{(hp)} = {\tau \text{(in} {\cdot} \text{lbf)} \times f \text{(rpm)} \over 63{,}025}</math>
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| The constant 63,025 is the rounded value of (33,000 ft·lbf/min) × (12 in/ft)/(2π rad/rev).
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| ==Current definitions==
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| The following definitions have been widely used:
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| {|class=wikitable
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| |-
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| |valign=top|[[#Mechanical horsepower|Mechanical horsepower]]<br />hp(I)
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| |≡ 33,000 [[feet-pound-force|ft-lb<sub>f</sub>]]/min
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| = 550 ft·lb<sub>f</sub>/s<br />
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| ≈ 17696 lb<sub>m</sub>·ft<sup>2</sup>/s<sup>3</sup><br />
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| = 745.69987158227022 [[Watt|W]]
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| |-
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| |valign=top|[[#Metric horsepower|Metric horsepower]]<br />hp(M) - also ''PS'', ''''cv, ''hk'', ''pk'', ''ks'' or ''ch
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| |≡ 75 [[kilogram-force|kg<sub>f</sub>]]·m/s<br />
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| ≡ 735.49875 W
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| |-
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| |[[#Electrical horsepower|Electrical horsepower]]<br />hp(E)
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| |≡ 746 W
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| |-
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| |valign=top|[[#Boiler horsepower|Boiler horsepower]]<br />hp(S)
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| |≡ 33,475 [[BTU]]/h
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| = 9,812.5 W
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| |-
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| |valign=top|[[#Hydraulic horsepower|Hydraulic horsepower]]
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| |colspan=2|= flow rate ([[US gal]]/[[minute|min]]) × pressure ([[lbf/in²|psi]]) × 7/12,000<br />
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| or<br />
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| = flow rate ([[US gal]]/[[minute|min]]) × pressure ([[lbf/in²|psi]]) / 1714<br />
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| = 550 ft·lb<sub>f</sub>/s<br />
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| = 745.69988145 W
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| |}
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| In certain situations it is necessary to distinguish between the various definitions of horsepower and thus a suffix is added: hp(I) for mechanical (or imperial) horsepower, hp(M) for metric horsepower, hp(S) for boiler (or steam) horsepower and hp(E) for electrical horsepower.
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| Hydraulic horsepower is equivalent to mechanical horsepower. The formula given above is for conversion to mechanical horsepower from the factors acting on a hydraulic system.
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| ===Mechanical horsepower===
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| Assuming the third [[General Conference on Weights and Measures|CGPM]] (1901, CR 70) definition of [[standard gravity]], ''g''<sub>n</sub>=9.80665 m/s<sup>2</sup>, is used to define the pound-force as well as the kilogram force, and the [[international avoirdupois pound]] (1959), one mechanical horsepower is:
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| :{|
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| |-
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| |1 hp
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| |≡ 33,000 ft-lb<sub>f</sub>/min
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| |colspan=3|by definition
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| |-
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| |= 550 ft·lb<sub>f</sub>/s
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| |since
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| |align=right|1 min
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| |= 60 s
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| |-
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| |= 550×0.3048×0.453592376 m·[[kilogram-force|kg<sub>f</sub>]]/s
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| |since
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| |align=right|1 ft
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| |= 0.3048 m and
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| |-
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| |= 76.0402259128 kg<sub>f</sub>·m/s
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| |align=right|1 lb
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| |= 0.453592376 kg
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| |-
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| |= 76.0402259128×9.80665 kg·m<sup>2</sup>/s<sup>3</sup>
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| |align=right|''g''
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| |= 9.80665 m/s<sup>2</sup>
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| |-
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| |= 745.699881448 W
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| |since
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| |align=right|1 W
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| |≡ 1 [[joule|J]]/s = 1 [[Newton (unit)|N]]·m/s = 1 (kg·m/s<sup>2</sup>)·(m/s)
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| |}
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| Or given that 1 hp = 550 ft·lb<sub>f</sub>/s, 1 ft = 0.3048 m, 1 lb<sub>f</sub> ≈ 4.448 N, 1 J = 1 N·m, 1 W = 1 J/s: 1 hp = 746 W
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| ===Metric horsepower (PS, cv, hk, pk, ks, ch){{anchor|Metric horsepower}}{{anchor|PS}}===
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| The various units used to indicate this definition (''PS'', ''cv'', ''hk'', ''pk'', ''ks'' and ''ch'') all translate to ''horse power'' in English, so it is common to see these values referred to as ''horsepower'' or ''hp'' in the press releases or media coverage of the German, French, Italian, and Japanese automobile companies. British manufacturers often intermix metric horsepower and mechanical horsepower depending on the origin of the engine in question. Sometimes the metric horsepower rating of an engine is conservative enough so that the same figure can be used for both 80/1269/EEC with metric hp and SAE J1349 with imperial hp.
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| [[Deutsches Institut für Normung|DIN]] 66036 defines one metric horsepower as the power to raise a mass of 75 kilograms against the earth's gravitational force over a distance of one metre in one second;<ref>{{cite web
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| |url = http://www.ptb.de/cms/fileadmin/internet/Themenrundgaenge/hueterin_der_einheiten/einheiten_d.pdf
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| |title = Die gesetzlichen Einheiten in Deutschland
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| |language = German
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| |page = 6
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| |trans_title = List of units of measure in Germany
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| |publisher = Physikalisch-Technische Bundesanstalt (PTB)
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| |accessdate = 13 November 2012}}</ref> this is equivalent to 735.49875 W or 98.6% of an imperial mechanical horsepower.
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| In 1972, the PS was rendered obsolete by EEC directives, when it was replaced by the kilowatt as the official power measuring unit.<ref>{{cite web
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| |url=http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=DD:I:1971_III:31971L0354:EN:PDF
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| |title=Council Directive 71/354/EEC: On the approximation of the laws of the Member States relating to units of measurement |publisher=The Council of the European Communities
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| |date=18 October 1971
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| |accessdate=3 March 2012}}</ref> It is still in use for commercial and advertising purposes, in addition to the kW rating, as many customers are still not familiar with the use of kilowatts for engines.
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| Other names for the metric horsepower are the Dutch {{lang|nl|''paardenkracht''}} (pk), the French {{lang|fr|''chevaux''}} (ch), the Russian {{lang|ru|Лошадиная сила}} (лс), the Swedish {{lang|sv|''hästkraft''}} (hk), the Finnish {{lang|fi|''hevosvoima''}} (hv), the Norwegian and Danish {{lang|da|''hestekraft''}} (hk), the Hungarian {{lang|hu|''lóerő''}} (LE), the Czech {{lang|cs|''koňská síla''}} and Slovak {{lang|sk|''konská sila''}} (k or ks), the Bosnian/Croatian/Serbian {{lang|sr|''konjska snaga''}} (KS), the Bulgarian {{lang|bg|Конска сила}}, the Macedonian {{lang|mk|Коњска сила}} (KC), the Polish {{lang|pl|''koń mechaniczny''}}, Slovenian {{lang|sl|''konjska moč''}}(KM) and the Romanian {{lang|ro|''cal-putere''}} (CP), which all equal the German {{lang|de|''Pferdestärke''}} (PS).
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| ====CV====
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| In addition, the capital form ''CV'' is used in Italy and France as a unit for [[tax horsepower]], short for, respectively, {{lang|it|''cavalli vapore''}} and {{lang|fr|''chevaux vapeur''}} (''steam horses''). CV is a non-linear rating of a motor vehicle for tax purposes.<ref>{{cite web|url=http://www.numericana.com/answer/units.htm |title=Measurements, Units of Measurement, Weights and Measures |publisher=numericana.com |date= |accessdate=2011-07-18}}</ref> The CV rating, or fiscal power, is <math>\scriptstyle\left(\tfrac{P}{40}\right)^{1.6} + \tfrac{U}{45}</math>, where ''P'' is the maximum power in kilowatts and ''U'' is the amount of carbon dioxide (CO<sub>2</sub>) emitted in grams per kilometre. The term for CO<sub>2</sub> measurements has been included in the definition only since 1998, so older ratings in CV are not directly comparable. The fiscal power has found its way into naming of automobile models, such as the popular [[Citroën 2CV|Citroën deux-chevaux]]. The {{lang|fr|''cheval-vapeur''}} (ch) unit should not be confused with the French {{lang|fr|''cheval fiscal''}} (CV).
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| In the 19th century, the French had their own unit, which they used instead of the CV or horsepower. It was called the [[poncelet]] and was abbreviated ''p''.
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| ===Electrical horsepower===
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| The horsepower used for electrical machines is defined as exactly 746 W. The nameplates on electrical motors show their power output, not their power input. Outside the United States watts are generally used for electrical power applications.
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| ===Drawbar horsepower===
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| :''See also [[Power at rail]]''
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| Drawbar horsepower (dbhp) is the power a [[railway]] [[locomotive]] has available to haul a [[train]] or an agricultural tractor to pull an implement. This is a measured figure rather than a calculated one. A special [[railway car]] called a [[dynamometer car]] coupled behind the locomotive keeps a continuous record of the [[drawbar (haulage)|drawbar]] pull exerted, and the speed. From these, the power generated can be calculated. To determine the maximum power available, a controllable load is required; it is normally a second locomotive with its brakes applied, in addition to a static load.
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| If the drawbar force (<math>F</math>) is measured in pounds-force (lbf) and speed (<math>v</math>) is measured in miles per hour (mph), then the drawbar power (<math>P</math>) in horsepower (hp) is:
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| :<math>P / {\rm hp} = {(F / {\rm lbf}) (v / {\rm mph}) \over 375}</math> | |
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| Example: How much power is needed to pull a drawbar load of 2,025 pounds-force at 5 miles per hour?
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| :<math>P / {\rm hp} = {{2025 \times 5 } \over 375} = 27</math>
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| The constant 375 is because 1 hp = 375 lbf·mph. If other units are used, the constant is different. When using a coherent system of units, such as [[SI]] (watts, newtons, and metres per second), no constant is needed, and the formula becomes <math>P = Fv</math>.
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| ===RAC horsepower (taxable horsepower)===
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| {{See also|Tax horsepower}}
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| This measure was instituted by the [[Royal Automobile Club]] in [[United Kingdom|Britain]] and was used to denote the power of early 20th-century British [[automobile|cars]]. Many cars took their names from this figure (hence the [[Austin Motor Company|Austin]] Seven and [[Riley (automobile)|Riley]] Nine), while others had names such as "40/50 hp", which indicated the RAC figure followed by the true measured power.
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| Taxable horsepower does not reflect developed horsepower; rather, it is a calculated figure based on the engine's bore size, number of cylinders, and a (now archaic) presumption of engine efficiency. As new engines were designed with ever-increasing efficiency, it was no longer a useful measure, but was kept in use by UK regulations which used the rating for [[tax horsepower|tax purposes]].
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| :<math>RAC h.p. = (D^2 * n)/2.5 \,</math>
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| :where
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| : ''D'' is the diameter (or bore) of the cylinder in inches
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| : ''n'' is the number of cylinders <ref>{{Cite web |url= http://www.designchambers.com/wolfhound/wolfhoundRACHP.htm |title= The RAC HP (horsepower) Rating - Was there any technical basis? |first= Richard |last= Hodgson |publisher=wolfhound.org.uk |accessdate=2007-08-11 |postscript=}}</ref>
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| This is equal to the displacement in cubic inches divided by 10π then divided again by the stroke in inches.
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| Since taxable horsepower was computed based on bore and number of cylinders, not based on actual displacement, it gave rise to engines with 'undersquare' dimensions (bore smaller than stroke) this tended to impose an artificially low limit on rotational speed ([[revolutions per minute|rpm]]), hampering the potential power output and efficiency of the engine.
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| The situation persisted for several generations of four- and six-cylinder British engines: for example, [[Jaguar (car)|Jaguar's]] 3.4-litre XK engine of the 1950s had six cylinders with a bore of {{convert|83|mm|in|abbr=on|sigfig=3}} and a stroke of {{convert|106|mm|in|abbr=on|sigfig=3}},<ref>{{Cite web |first= Dan |last= Mooney |url= http://www.classicjaguar.com/xkengine.html |title= The XK engine by Roger Bywater |publisher= Classicjaguar.com |date= |accessdate=2010-03-13 |postscript= }}</ref> where most American automakers had long since moved to oversquare (large bore, short stroke) [[V8 engine|V-8]]s (see, for example, the early [[Chrysler FirePower engine|Chrysler Hemi]]).
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| ==Measurement==
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| The power of an engine may be measured or estimated at several points in the transmission of the power from its generation to its application. A number of names are used for the power developed at various stages in this process, but none is a clear indicator of either the measurement system or definition used.
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| In the case of an engine [[dynamometer]], power is measured at the engine's [[flywheel]]. With a chassis dynamometer or ''rolling road'', power output is measured at the driving wheels. This accounts for the significant power loss through the drive train.
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| In general:
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| :[[#Nominal horsepower|Nominal]] is derived from the size of the engine and the piston speed and is only accurate at a pressure of {{convert|48|kPa|psi|0|abbr=on}}.<ref name=Brown>Brown, DK ''Before the ironclad'', pub Conway, 1990, p188.</ref>
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| :[[#Indicated horsepower|Indicated]] or gross horsepower (theoretical capability of the engine) [ PLAN/ 33000]
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| ::minus frictional losses within the engine (bearing drag, rod and crankshaft windage losses, oil film drag, etc.), equals
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| :[[#Brake horsepower|Brake]] / net / crankshaft horsepower (power delivered directly to and measured at the engine's crankshaft)
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| ::minus frictional losses in the transmission (bearings, gears, oil drag, windage, etc.), equals
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| :[[#Shaft horsepower|Shaft]] horsepower (power delivered to and measured at the output shaft of the transmission, when present in the system)
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| ::minus frictional losses in the universal joint/s, differential, wheel bearings, tire and chain, (if present), equals
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| :[[#Effective horsepower (ehp)|Effective]], True (thp) or commonly referred to as wheel horsepower (whp)
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| All the above assumes that no power inflation factors have been applied to any of the readings.
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| Engine designers use expressions other than horsepower to denote objective targets or performance, such as brake mean effective pressure (BMEP). This is a coefficient of theoretical brake horsepower and cylinder pressures during combustion.
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| ===Nominal horsepower===
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| Nominal horsepower (nhp) is an early 19th-century [[rule of thumb]] used to estimate the power of steam engines.
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| nhp = 7 x area of piston x equivalent piston speed/33,000
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| For paddle ships the piston speed was estimated as 129.7 x (stroke)<sup>1/3.35</sup>
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| For the nominal horsepower to equal the actual power it would be necessary for the mean steam pressure in the cylinder during the stroke to be {{convert|48|kPa|psi|0|abbr=on}} and for the piston speed to be of the order of 54–75 m/min.<ref name="Brown" />
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| ===Indicated horsepower===
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| Indicated horsepower (ihp) is the theoretical power of a reciprocating engine if it is completely frictionless in converting the expanding gas energy (piston pressure × displacement) in the cylinders. It is calculated from the pressures developed in the cylinders, measured by a device called an ''[[indicator diagram|engine indicator]]'' – hence indicated horsepower. As the piston advances throughout its stroke, the pressure against the piston generally decreases, and the indicator device usually generates a graph of pressure vs stroke within the working cylinder. From this graph the amount of work performed during the piston stroke may be calculated. It was the figure normally used for [[steam engine]]s in the 19th century but is misleading because the actual power output may only be 70% to 90% of the indicated horsepower.
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| ===Brake horsepower===
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| Brake horsepower (bhp) is the measure of an engine's horsepower before the loss in power caused by the gearbox, alternator, differential, water pump, and other auxiliary components such as power steering pump, muffled exhaust system, etc. ''Brake'' refers to a device which was used to load an engine and hold it at a desired rotational speed. During testing, the output torque and rotational speed were measured to determine the ''brake horsepower''. Horsepower was originally measured and calculated by use of the [[indicator diagram|"indicator"]] (a [[James Watt]] invention of the late 18th century), and later by means of a [[De Prony brake]] connected to the engine's output shaft.
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| More recently, an engine [[dynamometer]] is used instead of a De Prony brake. Although the output delivered to the driving wheels is less than that obtainable at the engine's crankshaft, a chassis dynamometer gives an indication of an engine's "real world" horsepower after losses in the drive train and gearbox.
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| ===Shaft horsepower===
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| Shaft horsepower (shp) is the power delivered to the [[propeller]] shafts of a [[steamship]] (or one powered by [[diesel engine]]s or [[nuclear power]]), or an [[aircraft]] powered by a [[piston engine]] or a [[gas turbine]] engine, and the rotors of a helicopter. This shaft horsepower can be measured with [[Measuring instrument|instrument]]s, or estimated from the indicated horsepower and a standard figure for the losses in the transmission (typical figures are around 10%). This measure is not commonly used in the [[automobile]] industry, because in that context drive train losses can become significant.
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| ==Engine power test codes==
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| Engine power test codes determine how the power and torque of an automobile engine is measured and corrected. Correction factors are used to adjust power and torque measurements to standard atmospheric conditions to provide a more accurate comparison between engines as they are affected by the pressure, humidity, and temperature of ambient air.<ref>Heywood, J.B. "Internal Combustion Engine Fundamentals", ISBN 0-07-100499-9 {{Please check ISBN|reason=Check digit (9) does not correspond to calculated figure.}}, page 54</ref> There exist several standards for this purpose, some described below.
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| ===Society of Automotive Engineers===
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| ====SAE gross power====
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| Prior to the 1972 model year, American automakers rated and advertised their engines in brake horsepower (bhp), frequently referred to as SAE gross horsepower, because it was measured in accord with the protocols defined in [[Society of Automotive Engineers|SAE]] standards J245 and J1995. As with other brake horsepower test protocols, SAE gross hp was measured using a stock test engine, generally running with few belt-driven accessories and sometimes fitted with long tube test [[Exhaust manifold|headers]] in lieu of the [[Original equipment manufacturer|OEM]] exhaust manifolds. The atmospheric correction standards for barometric pressure, humidity and temperature for testing were relatively idealistic.
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| ====SAE net power====
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| In the United States, the term ''bhp'' fell into disuse in 1971-72, as automakers began to quote power in terms of SAE net horsepower in accord with SAE standard J1349. Like SAE gross and other brake horsepower protocols, SAE Net hp is measured at the engine's crankshaft, and so does not account for transmission losses. However, the SAE net power testing protocol calls for standard production-type belt-driven accessories, air cleaner, emission controls, exhaust system, and other power-consuming accessories. This produces ratings in closer alignment with the power produced by the engine as it is actually configured and sold.
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| ====SAE certified power====
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| In 2005, the SAE introduced "SAE Certified Power" with SAE J2723.<ref>{{cite web|url=http://www.sae.org/certifiedpower/ |title=Certified Power - SAE J1349 Certified Power SAE International |publisher=Sae.org |date= |accessdate=2011-07-18}}</ref> This test is voluntary and is in itself not a separate engine test code but a certification of either J1349 or J1995 after which the manufacturer is allowed to advertise "Certified to SAE J1349" or "Certified to SAE J1995" depending on which test standard have been followed. To attain certification the test must follow the SAE standard in question, take place in an ISO9000/9002 certified facility and be witnessed by an SAE approved third party.
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| A few manufacturers such as Honda and Toyota switched to the new ratings immediately, with multi-directional results; the rated output of [[Cadillac|Cadillac's]] [[supercharger|supercharged]] [[GM Premium V engine#Supercharged|Northstar]] V8 jumped from {{convert|440|to|469|hp|kW|abbr=on}} under the new tests, while the rating for [[Toyota Motor Corporation|Toyota's]] [[Toyota Camry|Camry]] 3.0 L ''[[Toyota MZ engine#1MZ-FE|1MZ-FE]]'' V6 fell from {{convert|210|to|190|hp|kW|abbr=on}}. The company's Lexus ES 330 and Camry SE V6 were previously rated at {{convert|225|hp|kW|abbr=on}} but the ES 330 dropped to {{convert|218|hp|kW|abbr=on}} while the Camry declined to {{convert|210|hp|kW|abbr=on}}. The first engine certified under the new program was the 7.0 L [[GM LS engine#7.0 L|LS7]] used in the 2006 [[Chevrolet Corvette]] Z06. Certified power rose slightly from {{convert|500|to|505|hp|kW|sigfig=3|abbr=on}}.
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| While Toyota and Honda are retesting their entire vehicle lineups, other automakers generally are retesting only those with updated powertrains. For example, the 2006 Ford Five Hundred is rated at 203 horsepower, the same as that of 2005 model. However, the 2006 rating does not reflect the new SAE testing procedure as Ford is not going to spend the extra expense of retesting its existing engines. Over time, most automakers are expected to comply with the new guidelines.
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| SAE tightened its horsepower rules to eliminate the opportunity for engine manufacturers to manipulate factors affecting performance such as how much oil was in the crankcase, engine control system calibration, and whether an engine was tested with premium fuel. In some cases, such can add up to a change in horsepower ratings. A road test editor at Edmunds.com, John Di Pietro, said decreases in horsepower ratings for some '06 models are not that dramatic. For vehicles like a midsize family sedan, it is likely that the reputation of the manufacturer will be more important.<ref>Jeff Plungis, ''Asians Oversell Horsepower'', Detroit News</ref>
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| {{anchor|70020}}
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| ===Deutsches Institut für Normung 70020===
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| DIN 70020 is a standard from [[Germany|German]] [[DIN]] regarding road vehicles. Because the [[German language|German]] word for ''horsepower'' is '''''P'''ferde'''s'''tärke'', in Germany it is commonly abbreviated to ''PS''. DIN hp is measured at the engine's output shaft, and is usually expressed in [[#Metric horsepower|metric (Pferdestärke)]] rather than [[#Mechanical horsepower|mechanical horsepower]].
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| ===Economic Commission for Europe R24===
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| ECE R24 is a [[UNECE Regulations|UN standard]] for the approval of compression ignition engine emissions, installation and measurement of engine power.<ref>[http://www.unece.org/trans/main/wp29/wp29regs/r024r2e.pdf ECE Regulation 24, Revision 2, Annex 10]</ref> It is similar to DIN 70020 standard, but with different requirements for connecting an engine's fan during testing causing it to absorb less power from the engine.<ref>{{cite web|author=document.write(getDate()); |url=http://www.farmersjournal.ie/2003/0322/farmmanagement/machinery/tractor.htm |title=Farmers Journal: Tractor and machine comparison: what's the ‘true' measure - 22 March 2003 |publisher=Farmersjournal.ie |date=2003-03-22 |accessdate=2011-07-18}}</ref>
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| ===Economic Commission for Europe R85===
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| ECE R85 is a [[UNECE Regulations|UN standard]] for the approval of internal combustion engines with regard to the measurement of the net power.<ref>{{cite web|url=http://live.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/r085e.pdf |title=ECE Regulation 85 |format=PDF |date= |accessdate=2011-07-18}}</ref>
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| ===80/1269/EEC===
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| [[Directive 80/1269/EEC|80/1269/EEC]] of 16 December 1980 is a European Union standard for road vehicle engine power.
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| ===International Organization for Standardization===
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| * ISO 14396 specifies the additional and method requirement for determinating the power of reciprocating internal combustion engines when presented for an ISO 8178 exhaust emission test. It applies to reciprocating internal combustion engines for land, rail and marine use excluding engines of motor vehicles primarily designed for road use.<ref>{{cite web|url=http://www.iso.org/iso/catalogue_detail.htm?csnumber=32909 |title=ISO 14396:2002 - Reciprocating internal combustion engines - Determination and method for the measurement of engine power - Additional requirements for exhaust emission tests in accordance with ISO 8178 |publisher=Iso.org |date=2007-09-30 |accessdate=2011-07-18}}</ref>
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| * ISO 1585 is an engine net power test code intended for road vehicles.<ref>{{cite web|url=http://www.iso.org/iso/catalogue_detail.htm?csnumber=6179 |title=ISO 1585:1992 - Road vehicles - Engine test code - Net power |publisher=Iso.org |date=1999-11-15 |accessdate=2011-07-18}}</ref>
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| * ISO 2534 is an engine gross power test code intended for road vehicles<ref>{{cite web|url=http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=7476 |title=ISO 2534:1998 - Road vehicles - Engine test code - Gross power |publisher=Iso.org |date=2009-03-31 |accessdate=2011-07-18}}</ref>
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| * ISO 4164 is an engine net power test code intended for mopeds.<ref>{{cite web|url=http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=9932 |title=ISO 4164:1978 - Road vehicles - Mopeds - Engine test code - Net power |publisher=Iso.org |date=2009-10-07 |accessdate=2011-07-18}}</ref>
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| * ISO 4106 is an engine net power test code intended for motorcycles.<ref>{{cite web|url=http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=31406 |title=ISO 4106:2004 - Motorcycles - Engine test code - Net power |publisher=Iso.org |date=2009-06-26 |accessdate=2011-07-18}}</ref>
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| * ISO 9249 is an engine net power test code intended for earth moving machines.<ref>{{cite web|url=http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=38008 |title=ISO 9249:2007 - Earth-moving machinery - Engine test code - Net power |publisher=Iso.org |date=2011-03-17 |accessdate=2011-07-18}}</ref>
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| ===Japanese Industrial Standard D 1001===
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| JIS D 1001 is a Japanese net, and gross, engine power test code for [[automobile]]s or [[truck]]s having a spark ignition, [[diesel engine]], or fuel injection engine.<ref>{{cite web|url=http://www.webstore.jsa.or.jp/webstore/Com/FlowControl.jsp?lang=en&bunsyoId=JIS+D+1001%3A1993&dantaiCd=JIS&status=1&pageNo=0 |title=JSA Web Store - JIS D 1001:1993 Road vehicles - Engine power test code |publisher=Webstore.jsa.or.jp |date= |accessdate=2011-07-18}}</ref>
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| ==See also==
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| *[[Brake specific fuel consumption]]—how much fuel an engine consumes per unit energy output
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| *[[European units of measurement directives]]
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| *[[Horsepower-hour]]
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| *[[Torque]]
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| ==References==
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| {{Reflist|colwidth=30em}}
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| ==External links==
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| *[http://auto.howstuffworks.com/horsepower.htm How Stuff Works - Horsepower]
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| {{ISO standards}}
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| [[Category:Imperial units]]
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| [[Category:Units of power]]
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| [[Category:Customary units of measurement in the United States]]
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