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.
RSI Handbook: What are RSIs? A repetitive stress injury (RSI) is damage to body tissues -- muscles, tendons, spinal discs, blood vessels, and nerves -- caused by repeated physical stresses. RSIs are produced by a gradual build-up of tiny amounts of damage caused by repetitive motions involving the same few tendons or ligaments. Maintaining the same body posture for long periods of time -- as many jobs require -- contributes to developing RSIs, because such postures decrease blood supply to the working tissues, making it increasingly difficult for your body to repair itself.