The foot is a most easily accessible tool and it had a lengthy history as a means of measuring before the introduction of national and international standards. So how were earlier standards created? In this short video from 1981, the British physicist Reginald Victor Jones demonstrates a clever methodology for finding the length of an average foot illustrated in a 16th-century German geometry book. The video is excerpted from Jones’s 1981 Royal Institution Christmas Lecture series ‘From Magna Carta to Microchip’, a marvellously dated and humorously English account of the history and principles of measurement.