TDS Meter for Best Water Quality by TDS-Tech Measure Range 0-9990ppm, 1 ppm resolution, &plusmn;2% Accuracy! . Ideal for Water Hardness. Advanced CPU: Automatically calibrated temperature; 0 - 9990 ppm TDS tester measurement range with 1 ppm accuracy Hold Button: Holds measurement value when meter is removed from water for convenient reading and recording Temperature Button: Tests water in Celsius and Fahrenheit; 31 - 200 F degree range, 1 F degree accuracy Auto-Off Function: Shuts off automatically after 10 minutes of inactivity to conserve battery life Comprehensive: Great tool for testing hard water contaminated with arsenic, lead, aluminum and other metals