JamesT73J:
Do the numbers on the vibration gauge actually mean anything in terms of units, or is it just a guideline for the crew?
It's an indication. What you're looking for is *change* in vibration levels... I'm aware of cases where the Imminent Occurence of Something Nasty has been announced by a sudden *decrease* in vibration.
It's just one piece of evidence - you have to look at the bigger picture - EGT, N1/N2, EPR, fuel flow etc.
Also figures as a parameter in the engineers long-term engine trend monitoring, for failure prediction.
The 'units' are arbitrary numbers,
AFAIK.
R1