This is from some research I did a few months ago on the Captains clock vice CFDIU clock on our early model A319/320’s: (there just isn’t a whole lot of info on clocks out there)
“Interesting side light - I did read at some point in the past the wing tip brakes required a check every 9 days which was based on the CFDIU clock. If the Captains clock was set incorrectly it could lock out the wing tip brakes because the CFDIU clock would also be wrong. I also read without a clock the CFDIU is unable to print a post flight report. At some time those two things were changed so as to not rely on the Captains clock.”
Also our MEL allows for the Captains clock to be inoperative but not the CFDIU clock. If someone has some different information please share.
Tubby linton thank you for the excellent WTB explanation.