API gravity [American Petroleum Institute] (degree API, °API) petroleum processing A scale, expressed in degrees, for the volumic mass of petroleum liquids. Used for liquids less dense than water, it is structured identically with the Baumé scale for such liquids, except that it has its set temperature at 60°F rather than 10° Réaumur (12.5°C, 54.5°F); readings are thus about 1% greater than Baumé.
If S is volumic mass in kg·m −3 , and D is the API degrees, the two relate as follows: S × (131.5 + D ) = 141.5,  hence D = (141.5/ S
ok so its been so long sence ive visited the site i forgot my info and had to make a new profile. anyway im trying to change my front and rear diff. fluid and the book says to use api gls mti fully synthetic 75w90r so i went to the parts store to pick it up and they dont have it and they and i dont know what the r is for how ever they did have 75w90LS it was mobil 1 fully synthetic that said can i use it and what does all this API GLS MTI AND R stand for anyway. thanks for the help john.
