An apparatus for measuring movement of an object has a quadrature incremental encoder for providing first and second phases of encoder pulses corresponding to incremental displacements of the object. A first counter counts edges of the encoder pulses according to the sense of the displacement. Clock pulse counts are also made. Acquiring movement data at periodic speed processing moments includes the decoder adjusting encoder pulse data from the first counter using a clock pulse count that is a function of a lapse of time between when the most recent edge of the encoder pulses and the speed processing moment. The clock pulse counts are reset by edges of the first and second phases of the encoder pulses when the decoder acquires the movement data.