TN panel pivot useless
Summary
The pivot function of TFT displays is the ability to use such a display in portrait mode rather than landscape mode. The changed aspect ratio is useful in certain applications like editing book pages or editing source code. However when turning a display with TN-TFT panels, one recognizes a degraded image quality. This applies to all displays with a limited vertical viewing angle.
Here we just present the technical background for this phenomenon, but do not present a solution besides the suggestion to avoid using the pivot feature.
technical background
TFT displays and especially those with TN (twisted nematic + retardation film) panels have a limited viewing angle under which the contrast does not change. No display maintains the contrast over the full 180° view angle. In order to increase the practical usability the viewing angle of the x-axis is increased by means of a thin retardation film, while the viewing angle of the y-axis in reduced. The following screenshots are taken from [1]:
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vertical contrast difference is big with TN displays
Since your eyes are horizontally aligned a single pixel is seen from two different horizontal angles by both of your eyes. However the vertical viewing angle for both eyes is the same. This is depicted in the following two images:
both eyes see the same point by different x-axis viewing angles
both eyes see the same point by the same y-axis viewing angle
When using a TN display in landscape mode the different horizontal viewing angle doesn't really matter, since the contrast of TN panels hardly changes in the horizontal dimension. Both eyes see the same image with similar contrast.
However if you use the pivot function of your screen the bottom side becomes the left side of the screen. Now the contrast changes depending on your horizontal viewing angle. And since your eyes see the same image from two different horizontal angles your eyes you do see in fact two different images. If you move your head slightly in front of the screen you'll notice that your 2D screen looks as if text would be displayed in 3D. That impression is given to you since your imagination constructs shadows and others from the different contrast information collected by your eyes. Even without moving your head: This kind of image makes you dizzy. Using a TN display in portrait mode is not recommended.