This paper is about the development of a series of techniques to monitor the use, by farmers, of agrochemicals and fertiliser. It describes a system which we believe to be unique, not only to Europe but to anywhere else in the world. The system itself is basically simple and easy to understand. However, its significance requires some knowledge of the agricultural context to which the system has been applied. Since this paper has been prepared for a general conference of European researchers it is a reasonable assumption that many - perhaps most - readers will not be familiar, either with European agriculture or with the agrochemicals industry.