Over the dais in the great lecture hall of the Chemisches Unterrichtslaboratorium of the ancient University of Leipzig is the phrase ‘Gott hat alles nach zahl, masse und gewicht geordnet’ (God has ordered everything according to number, size and weight). This quotation was well appreciated by Justus von Liebig, the first of the great agricultural chemists, and he quoted it. The importance of quantitative measurement has indeed always been appreciated by scientists and is at the heart of the many disciplines that make up agricultural science. This is not to denigrate studies, the results of which can only be expressed in qualitative terms, or to minimise the importance of purely descriptive work; after all, discoveries of the life cycles of a parasite, or of the agent which causes a plant disease, are major scientific accomplishments. However, much of agricultural science is concerned with exploration of the many processes that might result in higher or more efficient growth and productivity of plants and animals. This necessarily entails measurement and the use of experimental method. The new technologies that enabled farmers to exploit favourably economic circumstances were dependent on the discovery of new ways in which to conduct and evaluate experiments. Furthermore, these discoveries, which facilitated agricultural productivity, have had considerable repercussions in other branches of science. Much of modern statistical technique and methodology, applied to such diverse subjects as quality control in manufacturing industry or assessment of the pathogenicity of microorganisms or the conduct of social surveys, originated in work carried out with improvement of agriculture in view.