Source: http://sites.nbed.nb.ca/wiki/ecc-sc/Bibliothques%20de%20documents%20du%20cours%20de%20mathmatiques/Bloc%201/Notes%20du%20Bloc%201%20C%20-%20Les%20syst%C3%A8mes%20m%C3%A9trique%20et%20imp%C3%A9rial.pdf