Is Horsepower Measured Using Horses ?????

"Horsepower" was invented by engineer James Watt. 

One horsepower unit ranges between 735.5 and 750 Watts (depending on whether the horsepower is mechanical, electrical, or metric)

Here’s how the story goes – Once upon a time when James Watt was working with ponies lifting coal at a coal mine, he wanted to have a form of measurement which would determine the power of the animal. Watt determined that a pony could do an average 22,000 foot-pounds of work 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 foot-pounds figure, which equals to 745 Watts. It is this figure which we see on our lawn mowers, cars, and even your vacuum cleaner sometimes.