This read-only object reports whether the AUM card's clock source has switched: noChange means the originally selected source is still active, clockSrcChanged means a failover or switch has occurred. An admin monitoring shelf timing stability would watch this object to be alerted whenever the card's clocking has changed sources, which is itself often a symptom of an upstream timing problem. Seeing clockSrcChanged would prompt the admin to check currentClock to determine what source the card switched to.