TEST YOUR WATER: How Pure is Your Water? With the push of a button, the TDS water tester can tell you your overall water purity level, which will be displayed on the screen in ppm (parts per million)EASY TO USE AND ACCURATE: Just stick it in about 1 inch of water instantly you get the reading. It's compact and doesn't need any maintenance. The TDS water tester is a rugged model that includes a protective carrying case with belt clipMEASUREMENT RANGE: 0-9990 ppm. From 0-999 ppm, the resolution is in increments of 1ppm. From 1000 to 9990 ppm, the resolution is in increments of 10ppm, indicated by a blinking 'x10' imageAUTO-OFF AND HOLD FUNCTION: The TDS tester shuts off automatically after 2 minutes of non-use to conserve batteries. Features a hold function that saves measurements for convenient reading and recording