An operating condition of a clock which is no longer locked to an input reference. In holdover, the clock maintains the same frequency and phase from when it was last locked to a reference.
Holdover begins when the clock is disconnected from the input reference. On Sentinel, that means when the GPS or the external 1PPS input has been removed.
Holdover terminates when the clock locks to a new reference input. On Sentinel, that means when the GPS or the external 1PPS input has been restored, and the Sentinel has re-locked to the input.