Function: Test different water qualities for optimal quality and temperature (cannot test pH or specific values of dissolved substances in water). Hold Function: Saves measured values for easy reading and recording. Auto Function: Turns off the meter after 10 minutes of inactivity to save battery life. Dual Range: The measuring range is 0 to 999 ppm with a resolution of 1 ppm. The measuring range is 1000-9900 ppm with a resolution of 10 ppm. Scope of application: This product can be used for water purifiers and filters, food (vegetables, fruits) and beverage quality control, swimming pools, spas, aquariums, and hydroponic systems. Specifications: Operating temperature range: 0-50°C. Hold function: Easy reading and recording. The measurement results are accurate, and you can check the water purity at any time at home. After 10 minutes of inactivity, turn off the device to save battery power. Press the "TEMP" button to switch between Fahrenheit and Celsius. Applicable industries: quality laboratories water, CDC, aquaculture, hospitals, swimming pools, and tap water quality testing. Please refer to the following water quality testing standards: 0 to 50 ppm --------- ultrapure water 50 to 100 ppm --------- pure water 100 to 300 ppm --------- ordinary pure water 300 to 600 ppm --------- Scale deposits may be present in the water. 600 ~ 1000 ppm --------- poor water quality Above 1000 ppm --------- non-potable water Specifications: Accuracy: ± 2% Measuring range: 0-9990 ppm Battery: 1.5V x 2 (button batteries) Temperature accuracy: ± 0.1°C Dimensions: 156 × 30 × 20 mm Package contents: 1 × TDS tester 1 × leather case 1 × instruction manual The instructions are available in Chinese and English. Please contact me for the French version. Note: This product only displays three digits. When the measurement result is greater than 999 ppm, the display will show "xxx x 10". For example, "2000" will be displayed on the screen as "200 x 10".