Oaktons Waterproof EcoTestr TDS Low is a convenient TDS meter that doesnt let dirt or moisture keep it from delivering accurate readings. It features a clear LCD display, a waterproof, dustproof housing, and automatic shutoff! It also has a self-adjusting TDS factor, allowing TDS measurement in an array of applications. Measures TDS from 0 to 1990 ppm with a resolution of 10 ppm. Unit measures 6 1/4" x 1 5/8" x 1 1/8" and includes four 1.5 V batteries that provide over 200 hours of use.