Conflicting Air Speed Indicator, (ASI), readings..

Have you noticed that when observing your air speed indicator in the cockpit view, then swopping over to the default, 6 instrument view, (with the "W" key), for a better view of the runway ahead, that the two readings are different, sometimes as much as 20-40 knots difference....?
(The cockpit view readings are generally the higher of the two).
This raises problems in trying to calculate the real stall speed when flaring out for a landing...
....!!
(Note: when flying prop planes with conventional analogue instruments).
...any comments...?
(Note that both sets of instruments are reading true air speed in knots)...?
Cheers all...
Paul.
(England).
(The cockpit view readings are generally the higher of the two).
This raises problems in trying to calculate the real stall speed when flaring out for a landing...

(Note: when flying prop planes with conventional analogue instruments).
...any comments...?
(Note that both sets of instruments are reading true air speed in knots)...?
Cheers all...
Paul.
(England).