The Coopers DIY Beer Hydrometer is a finely calibrated instrument used to accurately measure the density of your brew with respect to water. This measurement is referred to as the Specific Gravity (SG) of the liquid which can be used to test fermentation has ended and also assist calculate the alcohol content of your finished beer. The Coopers DIY Beer Hydrometer has been designed specifically for brewing beer and is made from high quality, robust food grade plastic to be accurate and avoid breakage. Not dishwasher safe.