Simple to use: Just switch on, Lower the cable down your well and the buzzer sounds when the probe contacts the water. Just read the depth off the cable to measure water level under ground. Easy to read: The cable is marked every meter with permanent plastic number tags colour coded to make reading even easier. Slim profile: the maximum diameter of the probe is 9mm allowing to be used where access is difficult. The unit is powered by a normal nine volt battery for long life and low cost operation.