1. The Total dissolved solids meter tester can be used in: water purifiers and filters, food (vegetable, fruits) & drink quality monitoring pools and spas hydroponics etc 2 Hold function: Saves measurements for convenient reading and recording. 3. Auto-off function: Turns off meter after 10 minutes of non-use to conserve batteries. 4. Press "TEMP" button can shift temperature meter between fahrenheit degree and centigrade degree. 5. Measures Range: 0-9990ppm, with a resolution of 1ppm. From 1,000 to 9,990ppm, the resolution is 10ppm, indicated by drinking x 10image, factory calibrated. 6. Applicable industries: water laboratories, CDC, the aquaculture industry, hospitals, swimming pools, household tap water quality testing.