In order to use the indicator with a variety of engines, various springs were furnished, some are shown :
These are calibrated to provide a known pen displacement as shown ;
This one provides one inch of vertical pen displacement for every 500 psi of engine cylinder pressure.
Once obtained, the Card (graph) was used by two distinct types of people. The Operating Engineer could visually inspect the Card and determine or detect; leaky piston packing, sticking piston, incorrect valve timing, loose bearings, restricted inlet and/or outlet piping and on and on. If the vertical and horizontal axis were truly represented the engine parameters (accurately scaled) the Plant Engineer could determine the efficiency and horsepower of the engine. The lines drawn on the card will form a closed shape, roughly a right triangle, and the area enclosed by this triangle represents WORK, as the engine SPEED was recorded by another device, POWER could be determined !!!!!!!!!