-Pilot gets in cockpit.
-As part of pre-flight procedures, pilot checks oil level on cockpit display.
-As per flight manual, pilot calculates minimum oil required for sectors ie base amount plus 'x' per flight hour. Note that on ETOPS sector an engineering check of levels required AS PART OF ETOPS sign off.
In the HIGHLY UNLIKELY case that oil level is less than required, maintenance release entry requesting oil addition.
Airyplane departs and arrives at destination.
Maintenance is required to monitor individual engines for adverse trends in oil consumption.
It ain't that hard.......
