Hydrometers are simple devices that rely on a precise weight to measure the density of the solution it’s floating it. In a solution of pure (distilled) water, weight in a brewer’s hydrometer allows the tool to float to a determined marking labeled as 1.000 specific gravity (SG) or 0 °Plato at either 60 °F (16 °C) or 68 °F (20 °C). (Homebrewers prefer specific gravity while professional brewers prefer the Plato scale.) Hydrometers are great for either original gravity (OG) or finishing gravity (FG). In this video learn how to use a hydrometer and also how to calibrate it so you can trust the results.