Recent......extract from Skybary:
"The term monitoring actually comes from the Latin root ‘Monere’ to warn and in the context of flight operations it is defined as:
The observation and interpretation of the flight path data, configuration status, automation modes and on-board systems appropriate to the phase of flight. It involves a cognitive comparison against the expected values, modes and procedures. It also includes observation of the other crew member and timely intervention in the event of deviation."
No hard and fast rules for when to intervene - common sense I guess - and please don't mention that there was a CCG in these modern times of self-awareness?
There go by the grace of God go I (?)