Alarms and indications should comply with the performance
standards for the Presentation of Navigation-related Information on
Shipborne Navigational Displays adopted by the Organization.
5.34.1 A means should be provided to alert the
user of "picture freeze".
5.34.2 Failure of any signal or sensor in use,
including; gyro, log, azimuth, video, sync and heading marker, should
be alarmed. System functionality should be limited to a fall back
mode or in some cases, the display presentation should be inhibited
(see fallback modes, section 9).