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.
Does your upper back ever feel tight, as though you have âknotsâ in it? You may have an upper-trapezius strain, a common repetitive stress injury (RSI). An RSI is a condition usually caused by placing too much stress or strain on a joint or musculoskeletal tissue. RSIs are often associated with performing recurring motions, whether on a computer, on the telephone or in a sports a...