This digital tool instantly checks overall water quality. TDS means Total Dissolved Solids, which includes any salt, metal, or mineral in the water. Pressing a button activates the TDS measurement, and the value is displayed on the screen in ppm (parts per million). The lower the TDS content, the purer the water, and pure water reads approximately 0 ppm. This device is suitable for checking tap water quality or determining when to replace water filters. (The meter does not test for biological contaminants.) This tool is used for drinking water, water filtration and purification, hydroponics (testing nutrients), aquariums, deionized water, swimming pools and spas, and commercial and industrial applications. The model features a durable design and includes a protective carrying case. This handheld TDS meter is suitable for commercial use. It includes a protective case with a belt clip function. Due to electronic circuitry and a built-in digital thermometer, measurement data can be stored for convenient reading and recording. The display features an easy-to-read LCD screen. This digital TDS water tester is suitable for testing applications such as hydroponics, swimming pools and spas, aquariums and reef tanks, water ionizers, and reverse osmosis systems. Measuring range: 0-9990 ppm Resolution: 1 ppm Accuracy: +/- 2% reading Power supply: 2 x 1.5 V (LR44 button battery) (not included) Colour: Black Material: Plastic Size: 155mm Package Contents: 1 x TDS Pen Only the above package content is included. Other items are not included. Note: Light and different displays may cause the color of the item in the photo to be a little different from the real thing.