to understand the ignition, injection timing and combustion events which occur near dead-center, when the engine piston and indicator drum are hardly moving Much better information during this part of the cycle is obtained by offsetting the indicator motion by 90 degrees to the engine crank, giving an offset indicator diagram. The events are recorded when the velocity of the drum is near its maximum and are shown against crank-angle instead of stroke. References Bibliography Pacey, A.J. & Fisher, S.J. (1967) "Daniel Bernoulli and the vis viva of compressed air", The British Journal for the History of Science 3 (4), pp. 388–392, British Transport Commission (1957) Handbook for Railway Steam Locomotive Enginemen, London : B.T.C., p. 81, (facsimile copy publ. Ian Allan (1977), ) External links Energy conversion Piston engines Steam power Thermodynamics Diagrams