Apparatus for synchronizing the spool speed between engines of a multi-engine aircraft having, for each engine, an electronic engine control (EEC) with a speed rating logic portion having an engine speed algorithm for calculating an EEC command speed signal (N sel) and a speed governing loop portion providing for commanding engine fuel flow in dependence on a command speed signal, includes a synchronizer reference unit (SRU) having the same engine speed algorithm used in the EEC, for calculating a independent SRU command speed signal for presentation to all EEC speed governing loops, alternatively with the individual engine EEC command speed signals, in response to operator control.