The International system of units is a system of units to help us write down quantities without having to use scientific notation or lots of digits or zeroes. For example, a million Hertz is a megahertz;
M. Roggenbach, L. Schröder, and T. Mossakowski. Recent Developments in Algebraic Development Techniques, 14th International Workshop, WADT'99, volume 1827 of Lecture Notes in Computer Science, page 146--161. Springer; Berlin; http://www.springer.de, (2000)
C. Olds, A. Lax, and G. Davidoff. Anneli Lax New Mathematical Library Mathematical Association of America, Washington, DC, (2000)Appendix I by Peter D. Lax.