Sprayers should be calibrated several times a year. Changes in operating conditions and the type of chemical used require a new calibration. Frequent calibration is even more important with liquid application because nozzles wear out with use, increasing the flow rate. For example, tests conducted at Ohio State University indicated that the flow rate of a 0.2 gallon-per-minute capacity brass nozzle increased by 10 percent after only three hours of use with a wettable powder material.
The same University of Nebraska survey indicate that 67 percent of the operators who calibrated before every spray operation had application errors below 5 percent while only 5 percent of those operators who calibrated their equipment less than once a year (once every two, three, four years) achieved the same degree of application accuracy.
Safety is extremely important when working with chemicals. Always wear gloves and protective clothing and follow label directions when handling chemicals and calibrating sprayers.