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