This dual-probe, commercial-grade monitor displays electrical conductivity or TDS readings for the “input” water (Line 1) and “output” water (Line 2).
The LDM-100R displays the difference in the two readings as "% Rejection."

FEATURES
Monitor the efficiency of contaminant removal by your RO membrane(s)
Dual line TDS/EC displays feed and product water (permeate)
Automatically calculates the % rejection
Blinking indicator at changeable % rejection reading
Extended battery life for continuous monitoring
Includes two sensor probes
Batteries included (two 1.5V AA)
On-screen battery life indicator
Designed for panel mounting.  Requires 20 mm diameter center hole.

PRODUCT DESCRIPTION
TDS Range: 0-9999 ppm or mg/L TDS; 0-10.0 ppt or g/L TDS
EC Range: 0-9999 Micro-siemen/cm2 (µS/cm2) EC; 0-20.00 Milli-Siemens/cm2 (mS/cm2) EC
Accuracy: +/- 2%
Resolution: from 0-99.9: 0.1 ppm or 0.1 µS/cm2
                 from 100-9999: 1 ppm or 1 µS/cm2
EC to TDS Factor: NaCl (0.5)
Auto Temperature Compensation (ATC) from 34 to 149°F (1 to 65°C)
Calibration: Each probe can be calibrated independently, digital to any point
Sensor: 1/2” NPT male threads
Sensor Cables: two 9.8 ft. (3 m) shielded cables
Battery Life: Approx. 2 years
Dimensions: 4.7 x 3 x 1 inch (12 x 7.5 x 2.6 cm)
Weight: 7 oz. (198 g) including batteries

Manufacture's Limited Warranty: One year from date of purchase.