HM Digital DM-1 In-Line Dual TDS Monitor, 0-9990 ppm Range, +/- 2% Readout Accuracy plastic Imported The DM-1 helps you tomeasure the tap water coming in vs the purified water going outof your water filtration system at any time The In-Line Dual TDS Meterdisplays TDS levelsof the feed water and product water with in and out electrode probes This TDS Monitor is highly efficient and accurate due to itsadvanced microprocessor technology 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 Installs quickly and easily