Abstract: A rotary position transducer comprises a sensor cooperating with a toothed wheel which has nominally evenly spaced teeth and which may, for instance, be mounted on the crankshaft of an internal combustion engine. The times at which the teeth pass the sensor are stored. The time intervals between consecutive teeth are calculated, for instance during fuel cut-off operation of the engine. An error in the angular spacing between consecutive teeth is calculated for the time interval between consecutive teeth, a time interval between further teeth disposed symmetrically about the consecutive teeth, and the nominal angular spacing between the further teeth.