Taylor Technologies 6028 Pool Test Kit, Electronic Watergram Calculator Solar-Powered That Calculates The Saturation Index Of Pool & Spa Water &bull; Fits in a pocket or wallet.&bull; Solar poweredno battery needed.&bull; Water resistant.&bull; Automatic shutoff.&bull; Automatic adjustment for cyanurate alkalinity.&bull; Fahrenheit and Celsius options.&bull; See the effect of changing any of the water balance factors instantly.&bull; Use for other basic math calculations.&bull; Calculator is the size of a credit card.