A320. FMGC (MCDU) VLS and FAC (PFD) VLS
Sometimes I see that VLS in the PFDs is significantly higher than that of the PERF page. It is easy to notice when there is little wind because there is less than 5 knots between VAPP and VLS in the PFD. When there is wind or MCDU VLS is higher than PFD's VLS, GS Mini masks the difference.
I have got used to routinely check the difference during every approach. Sometimes the effect in airplane's handling is very noticeably. Airplane will fly more during flare or it will sink, depending on which VLS is higher.
Most of the times, PFD VLS is a few knots lower than MDCU VLS, or they are the same, and only a few times PFD VLS is higher. I try to adapt the flare to that piece of information. If PFD VLS is higher, I retard somewhat later. If it is lower, I retard earlier.
However sometimes things don't happen as I expect.
And some particular airplanes in the fleet seem to always have a difference in the same sense, which makes me think there is some problem with the probes or something.
Some pilots add a few knots to the VAPP when MCDU VLS happens to be too slow compared to PFD's. But now we are not allowed to do that and I wonder why.