The electronic version of the Taylor Watergram Water Balance Calculator is a water-resistant solar-powered device that calculates the Saturation Index (SI) of pool and spa water and performs basic mathematical operations. Calculator is the size of a credit card. Features: Fits in a pocket or wallet. Solar powered-no battery needed. Water resistant. Automatic shutoff. Automatic adjustment for cyanurate alkalinity. Fahrenheit and Celsius options. See the effect of changing any of the water balance factors instantly. Use for other basic math calculations. Calculator is the size of a credit card.