This unit is highly efficient and accurate due to its advanced microprocessor technology. It has an Auto-Off function to conserve 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. It comes factor calibrated. and equipped with 3/8 in. & 1/2 in. Quick Connect T-fittings for Merlin Garden Pro™ or Tall Blue-Merlin™ for quick install. Measure the untreated water coming in vs. the purified water going out of your reverse osmosis system at any time. Limited 3 year warranty.