TDS-3: Handheld TDS Meter with Carrying Case With its rugged design and build, the TDS-3 is an ideal meter (tool) that can be used for any application; Ranging from water purification, to hydroponics to industrial waste water treatment. It comes with a black vinyl carrying case, protecting it when carried in a toolbox. FEATURES: Hold Function Auto-off Function (After 10 min.) Built-in digital thermometer Includes a carrying case with belt clip Factory Calibrated with a 342 ppm NaCl solution. (Meter can be recalibrated with a mini-screwdriver).