text: Except for tritium, which was determined by the helium gas emitted by radioactive decay, these measurements were taken using mass spectroscopy.
  * Deuterium (H / H) – , about 1 in 6420 hydrogen atoms
  * Tritium (H / H) –  = , measured on 16 September 1976, about 1 in 5.4010 hydrogen atoms
  * Oxygen-18 (O / O) – , about 1 in 499 oxygen atoms
  * Oxygen-17 (O / O) – , about 1 in 2640 oxygen atoms