The AquaFX Dual Inline TDS Meter displays TDS levels of the feed water and product water with "in" and "out" electrode probes. It is highly efficient and accurate due to its advanced microprocessor technology. Includes an auto-off function that conserves battery power, powering down the unit after 10 minutes of inoperation. Dual Range of 0-9990 ppm (from 0-999 pp the resolution is 1 ppm. From 1000-9990 ppm, the resolution is 10 ppm - indicated by a blinking "x10" image). The AquaFX Dual Inline TDS Meter is factory calibrated with a 342 ppm NaCl solution, and can be recalibrated using a mini-screwdriver. This meter comes equipped with quick-connect T-fittings, and installs quickly and easily. Specifications: Range - 0-9990 ppm, Accuracy - +/- 2%, Cable Length - 24.5" (including sensor), Fittings: 0.25" standard, Power Source - 2 x 1.5V button cell batteries (included), Battery Life - Approximately 1000 hours of continuous use, Weight - 2.8 oz.