HM Digital TDS-EZ Water Quality TDS Tester, 0-9990 ppm Measurement Range, 1 ppm Resolution, 3% Readout Accuracy plastic /100% Imported Economy model that is ideal for end-users. Highly efficient and accurate due to its advanced microprocessor technology. Hold Function: saves measurements for convenient reading and recording and battery life is approx. 1000 hours of usage and power source is 2 x 1.5V button cell batteries (included) (LR44 or equivalent) Auto-off function: the meter shuts off automatically after 10 minutes of non-use to conserve batteries. Display: large and easy-to-read LCD screen. Measurement 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' image. Fun, translucent blue housing that's very strong and durable. TDS-EZ meters are calibrated with a 342 ppm NaCl solution. Meters can be recalibrated with a mini-screwdriver. Includes a TDS chart sticker on the back of the meter that explains TDS values.