1. Apparatus for providing measurements indicative of sub-cyclic dynamic operating conditions of an internal combustion engine, comprising: speed sensing means responsive to rotation through successive small angles of revolution of a member of the engine for generating a signal for each occurrence thereof, said angles each being a small fraction of an engine cylinder stroke sub-cycle; means responsive to each signal of said speed sensing means for providing successive interval manifestations each indicating the time interval for revolution of the engine through the related one of said small angles; and processing means responsive to at least a pair of said interval manifestations related to each cylinder stroke for providing a measure of a dynamic operating condition of said engine.