| http://www.iso.ch/ | |
| http://metrology.corona.navy.mil/ | US Navy Metrology Home Page at NWAS |
| http://web.ansi.org/default.htm | American National Standards Institute |
| http://physics.nist.gov/cuu/Constants/index.html?/codata86.html | L'organismo che determina i valori delle costanti fondamentali: CODATA |