The Kalstein ATC Refractometer is a handheld, portable, milk refractometer with a milk scale that measures in the 0.0 to 20% range, is powered by ambient light, has ATC, an optical glass prism, and a durable metal body with rubber grip. A milk refractometer measures the refractive index of a solution in a sample, converts it to milk concentration in units of percent by weight (% milk, also known as degrees’ milk), and displays the results. Simply use provided pipette to apply couple of milk drops on the lens, the concentration is instant showing on the eye lens. Easiest Milk concentration tester on the market.