Function: Test the quality of different waters and make sure you enjoy the best water quality and water temperature ((The PH value or a specific value of a substance dissolved in the water cannot be tested). Hold Function: Saves measurements for easy reading and recording. Automatic Function: Turns off the meter after 10 minutes of non-use to save batteries. Dual Range: Measures from 0-999 ppm, with a resolution of 1 ppm to 1,000 at 9,900 ppm, the resolution is 10 ppm. Suitable: This item can be used in water purifiers and filters, monitoring food (vegetables, fruits) and beverage quality, swimming pools, spas, aquariums and hydroponics Note: The data is all manual measurement, please allow 1-77cm error due to the difference in light and display, there will be some color difference depending on the physical object received.