Abstract: A magnetic transducer (10) mounted on a turbine engine forms a sinusoidal signal N.sub.1 as the teeth of a gear (14) attached to the engine shaft pass the head of the magnetic transducer. One tooth of the gear is a "short tooth", having its tip slightly shaved, and acts as a reference point from which angular deviation is measured. The sinusoidal signal N.sub.1 is first presented to a AGC (24) to maintain the peak-to-peak amplitude of the sinusoidal signal within a predetermined range. A pulse generator (32) forms a spike pulse each time the short tooth passes the magnetic transducer (10). A comparator circuit (40) uses the spike pulse to enable a one shot (44) creating a reference pulse of a specific length. A counter circuit (48), clocked by a zero axis detector (50), is provided for ensuring that only one reference pulse is generated for each rotation of the gear (14).