English: Four men and their dog went to calibrate their spreader Doesn't quite rhyme like the song but the activity these men are engaged in is important. They are assessing a tray test for calibrating the spread pattern of a fertiliser spreader. A line of shallow trays are spread across the working width of a fertiliser spreader (usually 24m) The operator drives through the line of trays with the machine working. The trays are collected and the contents of each are tipped into a measure which will show the spread pattern density, depending on the type of machine being used. Adjustments to the settings can then be made if required. The basics are that fertiliser is very expensive and needs to be applied correctly without over or under dosing. There is also a legal requirement to prevent pollution of watercourses adjacent to field edges.