The digital selective calling (DSC) feature is a key part of the model 525. It must be connected to a GPS or Loran receiver to obtain the full capability of the DSC function for distress and routine hailing. A GPS "OK message appears on the LCD to confirm proper functioning of the GPS connection. The distress calling capability of the radio includes, in addition to the basic undesignated call, the ability to include information that designates the nature of the distress: fire, flooding, collision, grounding, capsizing, sinking, adrift, abandoning, piracy or man overboard. The operation of a VHF/DSC radio depends upon its ability to receive the digitally encoded hailing calls that are transmitted on channel 70. Therefore, the 525's receiver continuously scans for the very brief DSC hailing signals that are transmitted on channel 70 except when a signal is being received on a distress/hailing channel or a working channel.