The DM-1 helps you to measure the tap water coming in vs the purified water going out of your water filtration system at any timeThe In-Line Dual TDS Meter displays TDS levels of the feed water and product water with in and out electrode probesThis TDS Monitor is highly efficient and accurate due to its advanced microprocessor technologyHighly efficient and accurate due to its advanced microprocessor technologyAuto-Off function conserves battery power. The unit shuts off automatically after 10 minutes of non-useInstalls quickly and easily