A Hydrometer measures the weight of a liquid in relation to water. Sugar and other fermentable solids add density of the water, raising the specific gravity. As fermentation takes place, solids are converted to alcohol, lowering the gravity. Specific gravity is therefore a useful indication of fermentation prior to yeast introduction, and by comparison with beginning readings, an accurate final indication of the fermentation results.
Specific Gravity- 0.990 - 1.170, Balling or Brix 0-38% Sugar by Weight, Potential Alcohol by Volume 0-22%