Two positive displacement pumps are used to make a controlled solution mixture. Pump 1 is considered the lead and pump 2 the follower. The MS320 is used to control pump 2 at a ratio of pump 1. Utilizing the user unity ratio variable in the MS320, the ratio set point may be entered in user units. For example, if pump 1 always delivers 100 liters/min. and the application calls for the addition of between 5 and 20 liters/min of pump 2 solution. A ratio set point of 5.0 would equal 5 liters/100 liters and a ratio set point of 20.0 would equal 20 liters/100 liters.