TDS Meter Dual Mode Readings - Professional Grade - Easily Installs Inline - Very Simple To Use. Measure the tap water coming in vs. the purified water going out of your system at any time. Use the meter to determine when the filters need to be changed. Highly efficient and accurate due to its advanced microprocessor technology. Displays TDS levels of the Feed Water and Product Water with in & out electrode probes. Auto-Off function conserves 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 'x10' image. Factory calibrated meters are calibrated with a 342 ppm NaCl solution. Meters can be recalibrated with a mini-screwdriver. Comes equipped with 1/4 inch John Guest Quick-Connect T-fittings as shown. Also available with 3/8" fittings. Installs quickly and easily. Differences from the DM-1: Designed for commercial/industrial applications. Stronger, water-resistant casing. Improved design, including an extra large, easy-to-read LCD display. Longer, waterproof, shielded cables. Variable mounting bracket. SPECIFICATIONS: Range: 0-9990 ppm Accuracy: ±2% Cable Length: 46" (including sensor) Power source: 2 AAA batteries (included) Battery life: over 1000 hours of continuous use Size: 11.6 x 6.8 x1.8 cm (4.6 x 2.6 x .7in.) Weight: 201.3 g (7.1 oz.) HM Digital. Simply cut the line out from the RO membrane housing and install the inline probe between the membrane housing and the shutoff valve, when possible. The closer to the membrane housing the better. Insert the ends of the tube into the John Guest quick connectors on the TDS meter probe. Then cut the inlet feed water line to the system and install the other T/probe.