Hi there!
Nothing at all. Just nice to know..... FOR INFO
A large enough discrepancy should attract attention anyway and would probably become evident quite soon.
CHECK GW message should come up on MCDU if difference is more than 7t.
FCOM 4.6.20 p7 tells you what to do in this case:
"CHECK GW MESSAGE" appears on the MCDU when the gross weight computed by the FM and that computed by the FAC disagree by more than seven tons (16055 LB). When this message appears :
CALL UP the MCDU FUEL PRED page and CHECK the current GW (= main engine start weight from load sheet - fuel used) and correct it if necessary.
If the current GW on the MCDU is correct. (FM characteristics speed displayed on the MCDU are correct).
DISREGARD the computed FAC characteristics speed (VIs, F, S, Green Dot) and refer to speeds given in the QRH.
(FM characteristics speed displayed on the MCDU are correct).
If the load sheet seems to be the cause of the discrepancy
COMPARE FAC and QRH speeds, and select the most appropriate.