William of Malmesbury's "Deeds of the Kings of England" records that during the reign of Henry I "the measure of his arm was applied to correct the false ell of the traders and enjoined on all throughout England." The folktale that the length was bounded by the king's nose was added some centuries later. Watson dismisses William's account as "childish" but William was among the most conscientious and trustworthy medieval historians. The French "king's foot" was supposed to have derived from Charlemagne, and the English kings subsequently repeatedly intervened to impose shorter units with the aim of increasing tax revenue.