Horsepower-hour
A horsepower-hour is an outdated unit of energy, not used in the International System of Units. The unit represents an amount of work a horse is supposed capable of delivering during an hour. Based on differences in the definition of what constitutes the "power of a horse", a horsepower-hour differs slightly from the German "Pferdestärkenstunde" :
The horsepower-hour is still used in the railroad industry when sharing motive power. For example, if Railroad A borrows a 2,500 horsepower locomotive from Railroad B and operates it for twelve hours, Railroad A owes a debt of = 30,000 hp⋅h. Railroad A may repay the debt by loaning Railroad B a 3,000 horsepower locomotive for ten hours.
