Rainfall

Spotted this whilst walking the dog this morning.

It's a very simple rain gauge stuck on the top of a post. Presumably does the job as well as the farmer needs but it put me in mind of the weather predicting rope.

A simple measuring jug...but I spent the rest of the walk speculating how, why and in what circumstances this rainfall information is useful to the farmer? He can't do much about the amount of rainfall we get, can he?