The LAB-AIDS‚® 9 Level Conductivity Meter shows the relative conductivity/resistance of liquids and solids. As the conductivity of the tested material increases, the number of glowing red LEDs (light emitting diodes) will increase to a maximum of 8, which indicates a very good conductor. There will be zero glowing red LEDs if the material being tested has a very low electrical conductivity (is a good insulator). The 9 Level Conductivity Meter is well constructed. When treated with proper care and concern it should provide you with many hours of exemplary service. After each use, the probes should be thoroughly cleaned and dried. When storing, the 9V battery should be unsnapped from the battery posts. 1 9V battery is required, but is not supplied with the kit.