The VSMOW–SLAP scale is recommended by the USGS, IUPAC, and IAEA for measurement of deuterium and O concentrations in any substance. For O, a scale based on Vienna Pee Dee Belemnite can also be used. The physical samples, which are distributed by the IAEA and U.S. National Institute of Standards and Technology, are used to calibrate isotope-measuring equipment.
Variations in isotopic content are useful in hydrology, meteorology, and oceanography. Different parts of the ocean do have slightly different isotopic concentrations: δ O values range from –11.35‰ in water off the coast of Greenland to +1.32‰ in the north Atlantic, and δ H concentrations in deep ocean water range from roughly –1.7‰ near Antarctica to +2.2‰ in the Arctic. Variations are much larger in surface water than in deep water.