To overcome these problems, a new technique, called pulse-width modulation (PWM) flow control, was developed for flow rate control with conventional agricultural spray nozzles (Giles and Comino, 1989; 1990). Hans et al. (2000) used the correlations; to estimate the calculated flowrate, and the relative error to conduct flow rate calibration for solenoid operated sprayer nozzles. They developed characteristics curves of PWM settings for nozzle operations.