Its like having SONAR in the palm of your hand.   Many sailors say this is one of the most valuable tools they have on board.  It is about the size of a 2 cell flashlight, and is used by submersing it by hand, and pointing at the bottom.  Activating the spring loaded ON switch for a second or two will cause the night lighted LCD window to register the depth.  The reading will disappear after about 10 seconds when the unit is ready for another activation.  A transducer model has a 12 ft wire allowing operation from inside a boat or from a boat hook.
   The most common use by sailors is to survey an anchorage area by dinghy  for suitability.  The Depthmate may also be used for finding horizontal distances (2 to 240 ft) while scuba diving, and as a fish finder.  Uses one standard 9v battery.. SW 0.6 lbs.