A '''hydrometer''' is a device used to measure the specific gravity of unfermented wort and fermented beer during the [[Processes|brewing process]]. The most common form of brewing hydrometer is a hollow glass device with a metal weight at the bottom. A paper scale is included inside the tube, and usually marked in one or more scales. The hydrometer floats freely in the liquid you are measuring, and is read at the point where the surface of the liquid touches the stem. The most frequently used scale for brewing is the specific gravity scale. The [[specific gravity]] scale provides a relative measure of sugar as compared to water, and is typically expressed to three digits after the decimal point as in ''1.040''.