Specific Gravity, often dented as D20/20, and sometimes known as present gravity, is the density of beer or wort at standard temperature and pressure (20°C, 760 mm Hg) measured by saccharometer, hydrometer, or refractometer. A more accurate laboratory method is by weight using a specific gravity bottle. The units of specific gravity follow the practice of the country for original gravity, namely excess gravity, degrees Plato, degrees Balling, etc. In the case of unfermented wort, the specific gravity is the same as the original gravity. For fermenting wort or beer it is more correctly the apparent specific gravity that is measured by a saccharometer because the alcohol being lighter than water reduces the actual reading given by the floating bulb.