Are related terms for expressing the same basic idea. The difference between input horsepower and output horsepower is transmission loss. It may be stated as so much horsepower or it may be expressed as percentage of input horsepower. The ratio of output horsepower to input horsepower is called mechanical efficiency. It is usually expressed in percent. There is some loss of power for every bearing, sheave, gear, chain, belt wireline, stuffing box, fluid-drive and electric-drive.