Great Britain; Owen Ruffhead (1765). Statutes at Large. Printed by M. Baskett. p. 421. Consultado el 12 de febrero de 2012. «It is ordained that 3 grains of barley dry and round do make an inch, 12 inches make 1 foot, 3 feet make 1 yard, 5 yards and a half make a perch, and 40 perches in length and 4 in breadth make an acre.»