A microprocessor based control system including an electrical unit attached to a postmix beverage dispensing valve for performing the three functions of: portion control, reminding the operator to check the ratio, and adjusting the ratio. The portion control operation can be identical to known portion control devices. The reminder function can turn on a light every two weeks, for example. In the ratio adjusting function, the operator puts a single cup under the valve, pushes "Small" to dispense syrup for a predetermined time period which should result in the dispensing of a predetermined volume of syrup, measures the volume actually dispensed by comparing it to the desired volume, then adjusts the syrup flow control accordingly, and repeats the process until the exact predetermined volume is dispensed, and then repeats the steps for water using the same cup but a different predetermined volume indicia. The flow rate can accurately be set at the same time as the ratio.