Overview
The hydrometer is an instrument which is constructed on the Archimedes principle that a solid body displaces its own weight of the liquid in which it floats. Hydrometers can be divided into two general classes; namely for liquid heavier than water and for liquids lighter than water.
Plato Hydrometers with Thermometers
Calibrated to show the concentration of extract as a percentage by weight in brewery wort.
For example, a 5°P reading indicates 5 g of extract per 100 g of wort.
- Primarily used in the brewing industry
- Calibrated for use at 68°F/20°C
API ASTM Hydrometers with Thermometer
Chosen as the Standard Scale for Petroleum
The API Scale was selected as the standard hydrometer scale for petroleum products by the American Petroleum Institute (API),
the U.S. Bureau of Mines, and the National Institute of Standards and Technology (NIST).
- The API Scale is based on the following formula: °API @ 60°F = (141.5/(Specific Gravity at 60°F) - 131.5
- The thermometer scale is located in the body of the hydrometer
- Calibrated for use at 15°C/60°F
