Abstract: A first pair of DDAs for interpolating along a predetermined MAP-RPM-Fuel schedule for an internal combustion engine and a second pair for iterpolating along a predetermined MAP-TEMP-ENRICH schedule. Each DDA interpolates along a predetermind specific schedule for a number of iterations directly proportional to the magnitude of one of the engine dependent parameters comprising the schedule without necessitating any intervening conversion into or out of a binary number. The first DDA of each pair using slope and intersection data from a small memory interpolates linearly along at least two contiguous segments and feeds the second DDA which by feeding different register stages to different adders interpolates nonlinearly to effect a predetermined logarithmic relationship. The outputs of the two pairs are summed and then suitably clocked to selectively gate different fuel injectors.