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==History of development==
In 1916, the U.S. [[National Bureau of Standards]] accepted the [[Baumé scale]], which had been developed in France in 1768, as the U.S. standard for measuring the [[specific gravity]] of liquids less dense than [[Density of water|water]]. Investigation by the U.S. National Academy of Sciences found major errors in [[salinity]] and temperature controls that had caused serious variations in published values. Hydrometers in the U.S. had been manufactured and distributed widely with a modulus of 141.5 instead of the Baumé scale modulus of 140. The scale was so firmly established that, by 1921, the remedy implemented by the [[American Petroleum Institute]] was to create the API gravity scale, recognizing the scale that was actually being used.<ref>[http://www.sizes.com/units/hydrometer_api.htm API Degree history]</ref>
==API gravity formulas==
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*[http://dnr.louisiana.gov/assets/docs/oilgas/productiondata/comments_1989_rev.pdf Comments on API gravity adjustment scale]
*[http://www.globalsecurity.org/military/library/policy/army/fm/10-67-1/APPI.HTML Instructions for using a glass hydrometer measured in API gravity]
[[Category:Units of density]]
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