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.
Signs and symptoms of sacroiliitis may include: Pain and stiffness in your lower back, thighs or buttocks, especially in the morning or when sitting for a long period of time. Pain affecting your hips and shoulders. Pain that worsens with walking because the swinging motion of your hips strains your sacroiliac joints.igns and symptoms of sacroiliitis may include: Pain and stiffness in your lower back, thighs or buttocks, especially in the morning or when sitting for a long period of time. Pain affecting your hips and shoulders. Pain that worsens with walking because the swinging motion of your hips strains your sacroiliac joints.