Barkometers are used to measure the amount of tannin in a bark tanning solution through specific gravity and can tell you whether your solution is too weak to do anything, an appropriate strength for light, soft leathers, or strong enough for dense, heavy leather. It is an incredibly easy to use and useful tool, especially if you are using wild harvested tannins. A barkometer can also help you develop recipes for using your local tannin sources that can then be shared with others. Using my barkometer, I’ve found that 1 part crushed and ground Oregon White Oak galls to three gallons of water consistently makes a tannin solution with a barkometer reading within a degree or two of bk 10 … which is perfect for tanning light soft leathers.