Clapeyron, in his memoire, presented Carnot's work in a more accessible and analytic graphical form, showing the Carnot cycle as a closed curve on an indicator diagram, a chart of pressure against volume ( named in his honor "'Clapeyron's graph "').
12.
Horsepower was originally measured and calculated by use of the " indicator diagram " ( a James Watt invention of the late 18th century ), and later by means of a Prony brake connected to the engine's output shaft . More recently, an electrical brake dynamometer is used instead of a Prony brake.
