There are all sorts of parts to this: Coverage Do you use foam dots at the end of the boom, a dye included in the spray, GPS tracking? Speed Control Some sort of speedometer, a GPS speedometer, spray rate coupled to wheel speed, a calibrated foot? Nozzle Wear Do you have a calibration device to test the nozzles? System Flow How do you calibrate the pressure to the flow and how do you regulate it? Agitation How do you ensure the mixture stays mixed?