Abstract: A device for determining the volume of spraying liquid applied to unit area of ground by spraying equipment. The device includes pulse generators for generating first and second electrical signals respectively representing the rate of supply of liquid and the ground speed of the equipment. A function generating unit receives the two signals and, responding to these signals, produces an output signal representing the product of the ratio between the signals and a predetermined factor. The output signal from the comparator is applied to a meter which provides a visual indication of the output signal, this representing the volume of liquid applied to unit area of the ground. An automatic speed control unit can be coupled to an output from the function generating unit or to the means for generating the second electrical signal. This unit is actuated by an operator when the visual indicator indicates that a predetermined supply of liquid to unit area has been achieved.