Abstract: A computer, for use with a machine tool, can make any of a number of calculations involving ratios between two operands to determine the angular velocity of the spindle of the machine, the velocity and position of a movable member such as a carriage, and the ratio between two velocities. Any of such calculations is selected by means of a selector switch and a second selector switch is settable to select a time base for the calculation. The operands are represented by pulses produced by transducers associated with movable members of the machine tool.