The Hand Held Refractometers are specially designed for measuring the concentration of many kinds of solution listed as following: Juices, Beverages, Honey, Salt water, Brine, Cleaning fluid, battery fluid, Antifreeze and Industrial fluids etc. And they can also test for the proportion of the water-soluble solution. They can be easily used and they are competitive in price. You only need to drop some liquid on the prism and then make it towards to the sunlight. Then the reading of the concentration will appear. ATC means Automatic Temperature Compensation.