An indicated diagram is a graph between pressure and volume. The former being taken on vertical axis and the latter on the horizontal axis. This is obtained by an instrument known as indicator. The indicator diagram are of two types;
(a) Theoretical or hypothetical
(b) Actual.
The theoretical or hypothetical indicator diagram is always longer in size as compared to the actual one. Since in the former losses are neglected. The ratio of the area of the actual indicator diagram to the theoretical one is called diagram factor.
