Horsepower
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This article is about a unit of measurement. For the machine which used horses to generate power, see horse power (machine). For other uses of hp, see HP (disambiguation)
Horsepower (hp) is the name of several non-metric units of power. In scientific discourse, the term "horsepower" is seen as inferior and is rarely used because of its various definitions and the already existent SI unit for power, the watt (W). However, use of the term "horsepower" persists as a legacy in many languages and industries, particularly in the automotive industry because of their continued advertising of maximum power output of internal-combustion engines in "horsepower" units of measurement.
There are two important factors to consider when evaluating the measurement of "horsepower":
The inconsistent definitions of the "horsepower" unit itself
The various standards used in measuring the value of "horsepower"
These factors can be combined in unexpected ways ? the power output for an engine rated at "100 horsepower" might not be what a reader expects. For this reason, various groups have attempted to standardize not only the definition of "horsepower" but the measurement of "horsepower". In the interim, more confusion may surface.