Usage: Help you drink the safe and pure water, protect your health. Check the performance of your water filter and the hardness of the water you drink (1 grain =17 ppm). Dual Range : Measures form 0-999ppm, with a resolution of 1ppm. From 1,000 to 9,990ppm, the resolution is 10ppm, indicated by drinking x 10image, +/- 2% High Accuracy Features: The meter can lock the readings to help you read and record. Turns off meter after 10 minutes of non-use to save batteries Easy to Carry:The testers is lightweight ,rasy to storage and portable.It fit in your pocket and you can take it anywhere. Please note: This meter CANNOT calibrate, It can be used in : water purifiers and filters, food (vegetable, fruits) & drink quality monitoring, pools and spas, aquariums, hydroponics.