Indicator diagram and indicated power:

An indicated diagram is graph between pressure and volume. The former being taken on the vertical axis and latter on the horizontal axis. This can be obtained by an instrument called as indicator. The indicator diagrams are of two types;

(a) Theoretical or hypothetical

(b) Actual.

The theoretical indicator diagram is always longer in size as compared to actual one. As in the former losses are neglected. The ratio of area of actual indicator diagram to theoretical one is called as diagram factor.