The 250m Solinst 101D Water Level Meter with Drawdown functionality is used for measuring the water level in deeper bores. The Drawdown functionality is useful when you want to limit the maximum drop in the water while purging or pump testing. The instrument has a combined on/off and sensitivity adjustment dial. The probe is 16mm in diameter by 137mm long, rated to 300m submersion and connected to a 10mm wide flat laser marked tape. The unit is powered by an easily replaceable 9V alkaline battery.