What is the best way to measure specific gravity?

One way to determine when Metal Rescue is used up is to measure specific gravity. There are many ways to measure specific gravity. One way is to use a hydrometer. They are easily available and cost between $5 and $15. They are commonly used for home brewing and wine making, and also used by people who keep salt water aquariums. Additionally, most manufacturing facilities with labs or chemicals have several ways to measure the specific gravity of a liquid.