One of the most important standards that the API has set is the method used for measuring the density of petroleum. This standard is called the API gravity. Specific gravity is a ratio of the density of one substance to the density of a reference substance, usually water.
The most common symptoms of RSI include: 1  Pain. 2  Tingling. 3  A feeling of restlessness in the joint. 4  Weakness. 5  Throbbing. 6  Stiffness or cramp.
Repetitive strain injury (RSI) is most commonly related to the overuse and strain on the muscles, tendons and soft tissues of the upper part of the body like the wrists, forearms, shoulders, elbows, back or neck.