TDS Water Quality Test Pen: Professional TDS, EC and temperature pen. Upgraded with a Big Backlit LCD display for easier reading and auto-lock function for easier use TDS Meter Water Quality Tester: Feature a hold function that records measurements for convenient reading and recording. Precise High Accuracy Test Pen: TDS stands for Total Dissolved Solids, which are the inorganic salts and organic matter in a liquid. This includes Calcium, Magnesium, Sodium, etc. LCD Display Water Tester: With the press of a button, the TDS can tell you your overall water purity level, which will be displayed on the screen of PPM. Drinking water meter: To achieve accuracy, equipped with a premium titanium alloy probe and reliable automatic temperature compensation (ATC) ensures consistently accurate reading at various temperatures