a pumping mechanism moving in movement increments is controlled to space those movement increments in direct proportion to the volume resulting from each movement increment . in a further aspect , movement increments are grouped to result in approximately equal volumes per group . the mechanism moves continuously through the movement increments in each group . groups are spaced to result in approximately equal flow volumes per group . the number of groups decreases as the flow rate increases . the number of movement increments in each group and the volume of each group increase as the flow rate increases .