A calibration device (2) that utilises sensor data from an optical sensor to develop one or more calibration parameters for controlling operation of a sprayer (15) utilising itself optical sensors (19) and transmitting the calibration parameters to said sprayer. A method of calibrating a sprayer utilising the calibration information is also disclosed. A method of pasture or crop management for a region of interest in which a composite representation of cumulative substance applications is used to developing a representation in which sub regions of the region of interest having prescribed characteristics are visually differentiated from other regions. The spatial distribution of calibration values may also be recorded and used to analyse substance application against calibration values to develop a report of apparently anomalous calibration values.
