A TDS Meter and Digital Thermometer measures the amount of Total Dissolved Solids (TDS) in a solution. Since dissolved ionized solids like salts and minerals contribute to the conductivity of a solution, a TDS meter measures the conductivity of the solution which is then converted to a TDS reading. TDS is directly related to quality of water i.e., the lower a TDS figure, the more pure the water. As an example, reverse osmosis purified water will have a TDS between 0 and 10, whereas tap water will vary between 20 and 300. The D-D TDS meter is supplied pre calibrated . Measures TDS from 0-9999 ppm ( 0-1000 in increments of 1ppm, 1000-9999 in increments of 10ppm) Long battery life with auto shut off feature Automatic temperature compensation Highly accurate Supplied complete with carry case Essential equipment for monitoring RO unit production and the remaining life of Di resin.