As has been discussed ad infinitum on other threads, you cannot always see what input is being made to the opposite sidestick.
If a sidestick had been replaced and wired up backwards (it has happened), then the sidestick might be moved say full left but the controls might go full right. Or a flight computer might have a fault which reverses the sidestick inputs. By crosschecking the maltese cross with the flight control page, I am double checking that the sidestick direction and the flight controls are moving in the same sense.
My original answer to the OP was:
During the control check, one pilot will move their sidestick to the limit in all directions in sequence. The other pilot watches this and checks that the correct flight controls, (ailerons, spoilers, elevators and rudder), move the correct amount in the correct direction on the flight control page,
which seems pretty clear to me?
U