Wide Usage:TDS tester can be widely used in water purifiers and filters, food (vegetables, fruits) and beverage quality control, swimming pools and spas, aquariums, hydroponics, etc. Three test modes: The measurement principle of TDS meter is to measure the conductivity of water which indirectly reflects the TDS value. With the hold function, you can save the measurement results, read and save. Three test modes: ON/OFF is the switch button, HOLD is the lock button, and TEMP is the mode key that can be adapted to personal needs. Easy to use:The tester TDS can detect some impurities in water, like soluble salts, ionic organic compounds, heavy metal ions, etc., which provides great convenience for you and your family to get cleaner water. No matter where you are, travel/game/shopping, check the TDS value of water at any time with 2% measurement accuracy. Auto-off function: If no operation is performed for 5 minutes, the TDS tester will automatically shut down to save power. To prevent the battery from being drained. Measurement range:0-9990ppm, resolution is 1ppm. From 1000 to 9990 ppm, the resolution is 10 ppm. Note: The TDS pen cannot be used to measure water with high temperature (such as hot water) or to measure water with strong shaking.