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A quad is a unit of energy equal to 1015 (a short-scale quadrillion) BTU, or 1.055 × 1018 joules (1.055 exajoules or EJ) in SI units.
A horsepower-hour (hph) is an outdated unit of energy, not used in the SI system of units. The unit represents an amount of work a horse is supposed capable of delivering during an hour (1 (one) horsepower integrated over a time interval of 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" (PSh):