Highly efficient and accurate due to its advanced microprocessor technology. Auto-Off function conserves battery power. The unit shuts off automatically after 20 seconds. Dual range – measures from 0-999 ppm, with a resolution of 1 ppm. From 1000 to 9990 ppm, the resolution is in 10 ppm increments, indicated by a blinking image. Comes factory calibrated. Comes equipped with 3/8 in & 1/2 in Quick Connect T-fittings for Evolution RO1000, PreEvolution, Merlin Garden Pro or Tall Blue for quick install. Measure the untreated water coming in vs. the purified water going out of your reverse osmosis system at any time.