TDS meter tester for testing the purity of water from filters Helps you to drink safe and pure water and protect your health Hold function: readings can be locked for easy reading and recording. and allows for one quick measurement in 5 seconds. Dual range: Measures from 0-999ppm with a resolution of 1ppm. measures from 1,000 to 9,990ppm with resolution in 10ppm increments, indicated by a flashing 'x10' image. Easy to use: Simply turn on the TDS meter and gently agitate the water, then a steady reading will automatically lock onto the LCD within 10-30 seconds, if not operated for more than 10 minutes the meter will automatically switch off to save battery. Wide range of applications: Check the performance of your water purifier and the hardness of your water. Use in water purifiers and filters, aquariums, hydroponics, beverage quality monitoring, swimming pools and spas.