1.The Digital TDS Water Meter is ideal for testing applications such as hydroponics and gardening, pools and spas, aquariums and reef tanks, water ionizers, Water Filter. drinking water and more. 2.Measurement Range: 0-9990 ppm , 1 ppm Resolution, +/- 3% Accuracy. 3.Temperature Button: Test water temperature, 31 – 200 F degrees, 1 F degree resolution.Hold 4.Function: saves measurements for convenient reading and recording. 5.Auto-off function – Turns off meter after 10 minutes of non-use to conserve batteries. 6.The smallest and lightest TDS meter available on the market.Highly Efficient and Accurate Due to Its Advanced Microprocessor Technology. 7.Power source: 2 x 1.5 V(LR44 Button Cell