Delarocha is totally correct which should be almost meaningless to anybody but an engineer who designs and developed the engine and its accessories.. .. .The user of the engine simply needs to understand relative experience which equates to soothing hums from the engine or your instrumennt dials and eyeballs jiggering so badly that you are convinced somethings going to break unless you shut it down promptly. Everything else in between is subjective and relates to time at the condition.