With positional accuracy being substantially improved through the use of DGPS guidance, the aerial application industry is now focussing on controllers to improve deposit uniformity and accuracy. Flow controllers that maintain constant application rate by modifying flow in response to varying ground speed are beginning to appear on the market. This report evaluates one such system, Auto Cal, used during simulated and operational programs in hilly terrain. For simulated insecticide treatments (application rates 2.4L/ha) delays of 2-5 seconds from flow initialization were observed before application rate stabilized to within 2% of calibration. Application rates were maintained to within 2% along the spray line despite ground-speed changes of 15%. During an operational herbicide program, block average application rate was again maintained within 2% of calibration resulting in reduced pesticide use. Improved treatment uniformity was apparent when compared to a non-controlled scenario. Problems encountered during these trials are discussed and recommendations for improvements made.