HM Digital Aquapro TDS Water Tester Model AP-1 Measures total dissolved solids (TDS) and temperature. Automatic Temperature Compensation (ATC) Water-resistant housing Measurement Range: 0-5000 ppm Digital Calibration (push button) Auto-off function, data-hold function and low-battery indicator. Display: large and easy-to-read LCD screen includes simultaneous temperature reading. Factory Calibrated: The AquaPro is calibrated with a 342 ppm NaCl solution. The meter can be recalibrated with digital calibration using the push buttons, rather than a screwdriver. Includes a cap and batteries. One year warranty.