Specific gravity is an important factor when purchasing a level probe. A float will rest higher or lower in a liquid depending on the liquids density or specific gravity.
Water is the reference liquid for density, with a specific gravity of 1. Less dense liquids will have a smaller specific gravity, such as propane at 0.5. Higher density materials have a higher specific gravity. For example, Mercury at room temperature has a specific gravity of 13.63.
Simply put, specific gravity for liquids works a little like this: less than water is less dense, greater than water is more dense.
At APG, we design our floats to show level where the center of the float rests. If the float is too high or too low in the liquid, this will introduce inaccuracy into the application.