The image above shows a P-V, or Pressure-Volume, diagram for an ideal and typical gasoline engine. It shows, visually, what's going on in your engine as it burns gasoline.

The result is a steam pressure-volume diagram which is used to measure the efficiency and other attributes of the steam engine. The introduction of this steam indicator in the late 1790s by James Watt ...

The result is a pressure-volume diagram of the engine while in operation, and engineers can measure and adjust the engine's properties under real time varying load conditions.

Not until 60 years after 1899 Otto Frank's mathematical formulation of the volume-pressure diagram and his concept of the mechanism of the cardiac work of the left ventricle cardiophysiologists began ...