This object reports how long, in seconds, the system clock spent in its most recent holdover period, the interval during which it had lost its external reference and was coasting on its own internal oscillator's stability instead. It is a key historical indicator of timing reliability: frequent or lengthy holdover events suggest an unstable upstream reference or flaky physical link, which matters greatly for any application depending on precise timing, such as cellular backhaul or TDM circuit emulation. A value of 1800 (30 minutes) for the last holdover would flag a fairly serious, sustained reference-loss event worth investigating, versus a value of 5 indicating only a brief blip.