The controller of the plural component proportioner (10) dispenses both components (or all three if a three component material) simultaneously (at least initially) and maintains ratio at the end of each predetermined volume of material by determining which component pump (12) has reached the desired amount of travel (given the resolution available) and using a valve (16) to shut off output of that pump until the other side has caught up. At pump changeover, the output valve for that pump (12) is shut off and the air motor (12a) allowed to run until travel stops to account for cavitation, air entrainment, compressibility, or poor inlet check performance.