This object reports which of the three possible clock sources — primary (described by pxmPrimaryMuxClockSource), secondary (described by pxmSecondaryMuxClockSource), or the card's internal oscillator — is currently actually selected and driving the PXM card's timing. An admin cares because this is the live answer to 'what clock is this card actually running on right now,' which can differ from the configured primary if a failover to secondary or fallback to the internal oscillator has occurred. For example, seeing intOscillator(3) here when the chassis is supposed to be synced to an external primary reference is a strong signal that both primary and secondary clock sources have failed.