This HM Digital DM-1: In-Line Dual TDS Monitor is a Pure Water Meter that tests water quality for Total Dissolved Solids of your incoming and out going water lines. This Monitor: *Displays TDS levels of the feed water and product water with in and out electrode probes. *Highly efficient and accurate due to its advanced microprocessor technology. *Auto-Off function conserves battery power. The unit shuts off automatically after 10 minutes of non-use. *Dual Range 0-9990 ppm (From 0 - 999 ppm the resolution is 1 ppm. From 1000 to 9990 ppm, the resolution is 10 ppm, indicated by a blinking 'x10' image.) *Factory Calibrated: our meters are calibrated with a 342 ppm NaCl solution. Meters can be recalibrated with a mini-screwdriver. *Comes equipped with John Guest Quick-Connect T-fittings as shown. *Installs quickly and easily.