introduce: TDS is an abbreviation for Total Soluble Solids. The TDS value represents the impurity content of the dissolved matter in the water. The greater the TDS value, the greater the impurity content in the water, and the less the impurity content. how to use: Remove the pen holder and turn on the ON switch; Put the pen into the test solution, the height of the solution should not exceed 2cm; Stir the pen in the solution until the reading is stable (2-6 seconds), the TDS value will be displayed on the screen, then press the HOLD key to lock the value. After use, wipe off the water on the pen, rinse with pure water, and then cover the pen. Precautions: Avoid immersing the TDS pen body in water, avoid direct sunlight, keep away from high temperature, avoid heavy impact and drop touch.