FicBox TDS-4 Pocket Size TDS Tester Meter Without Digital Thermometer, 0-9990 ppm Measurement Range , 1 ppm Resolution, +/- 2% Readout Accuracy This TDS tester is ideal for all water purification applications, wastewater regulation, aquaculture, hydroponics, and colloidal silver ATC (Automatic Temperature Compensation) The Sleek design of the TDS-4 is perfect for personal or commercial use Advanced microprocessor technology Hold Function: Freeze the measurement to view it out of the water.