The HM Digital TRM-1 TDS Meter allows you to take 3 different readings Ideal for window cleaners and aquarists that want to monitor water input TDS, Reverse Osmosis Output from the first DI Stage 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 Comes equipped with Mur-lok Quick-Connect T-fittings. Quick and Easy to instal!