Abstract: Computing apparatus for producing a digital output equal to ##EQU1## where N.sub.1 is a preset digital factor and V.sub.1 and V.sub.2 are analogue input signals. The apparatus includes a pulse generator arranged to receive in turn each of the signals V.sub.1 and V.sub.2 and to generate pulses at a frequency proportional to the magnitude of the signal, a counter for counting pulses received from the generator, timing means for measuring the time T taken for the count in the counter to reach the value N.sub.1 when signal V.sub.1 is applied to the pulse generator, means for resetting the counter, and means for extracting the count in the counter after a time equal to time T has elapsed during a counting operation with signal V.sub.2 applied to the pulse generator.