Note:Our 5-in-1 PH TDS meter has been calibrated by factory, you can use it directly. And after long time of use, if the error of the measured value is large, it can be calibrated by calibration solution as needed. Whats 5 in 1 PH Meter: Test Acidity Alkalinity of water, TDS : Total Dissolved Solids, can test the contaminants, EC : Electrical Conductivity, can be used to measure soluble ion concentrations in liquid fertilizers or growing media, SALT : test Salinity, and Temperature test. Measuring Range:PH 0.00-14.00 (0.01PH accuracy), TDS 0-10000ppm, EC 0-10000uS/cm, and temperature 0-60. LCD Backlight Display :This PH meter is designed with a clear LCD green backlight screen that displays the information in an intuitive layout. You can still read the digital even in a low visibility situation. WIDE APPLICATION:This 5-in-1 multi-functional TDS tester is ideal for home and laboratory pH testing applications, which can be used to test the quality of drinking water, swimming pools, aquariums, and home planting.