The Baum scale is actually two independent and mutually exclusive (non-overlapping) hydrometer scales that cover (a) liquids with a specific gravity greater than 1.0 and (b) liquids with a specific gravity less than 1.0. Note: The Baum scale is NOT a temperature scale. Named for its inventor, Antoine Baum (1728-1804), the Baum scale is actually two scales, one for liquids that are more dense (heavier) than water and one for liquids that are less dense (lighter) than water. The hydrometers are calibrated using the following rules: For liquids heavier than water: 0 B = distance the hydrometer sinks in pure water; 15 B = distance the hydrometer sinks in a solution that is 15% sodium chloride (salt, NaCl)by mass. For liquids lighter than water: 0 B = distance the hydrometer sinks in a solution that is 10% sodium chloride (salt, NaCl)by mass. 10B = distance the hydrometer sinks in pure water. To convert from B to specific gravity at 60degrees Fahrenheit: specific gravity= 145/ (145 - B). Remember: you MUST specify whether you are using the "heavy" or "light" scale when stating a Baum value. The two scales cannot be interconverted - they DO NOT overlap. For example, 25 B (heavy) and 25 B (light) are NOT the same!! The Baum scale does not directly measure the concentration of a solution. For example, to determine the concentration of nitric acid from a hydrometer reading, you would need to determine the specific gravity and then utilize a table of known specific gravity values for nitric acid at known concentrations. The Baum scale has traditional usage in industries where hydrometer readings have long been used to indirectly determine the concentration of a solution. Examples include brewing, wine-making, honey production, and acid production. However, hydrometers and pycnometers can also read specific gravity directly, so use that instead of Baum. It is a LOT less confusing to have only one scale (specific gravity) rather than two similar, confusing and non-overlapping scales (Baum)! MSDS Relevance: You may find this term used on MSDS's for concentrated acids  or sugar-containing liquids used by the brewing industry. We consider the Baum scale to be archaic (old, outdated) and confusing (because it is really two different scales that do not overlap). We discourage its use anywhere, particularly on MSDS's! By OSHA regulation, the specific gravity is required information on an MSDS. See also: Mass Units,Volume Units