Anyone who has ever had occasion to make accurate linear measurements is likely to be familiar with the vernier scale. I learned only recently that this scale is (or was formerly) also called a “nonius”. The 16th century Portuguese astronomer and mathematician Pedro Nunes was the first to use several slightly different scales, to obtain more accurate measurements with an astrolabe. Nunes’s system was adapted and simplified by the French mathematician Pierre Vernier. “Nonius” is a latinized form of Nunes’s name, and has fallen into disuse in English. In some languages (Spanish, Italian, Portuguese) the name nonio is still used, in preference to vernier ( both names are often written in lower-case).