Abstract: A method for determining a time interval between leading edges of two adjacent cyclic input pulses of a series of cyclic input pulses. A sample of the cyclic input pulses is taken at each of a series of sampling times to produce sampling hits, each sampling hit being an indication of a presence of a cyclic input pulse, recording a count number at each of the sampling hits, determining initial sampling hits from the detected sampling hits, determining a minimum sampling interval between initial sampling hits, and determining a count number located at a back end of the minimum sampling interval, count numbers of the minimum sampling interval being used to determine a time interval between lead edges of two adjacent cyclic input pulses.