If the image on the back side is skewed, change the back side.
If the image on the front side is skewed, change the front side.
The leading edge of the sheet and the top-left corner. a in the figure above.
For example, the distance is 10.3 mm (0.40").
The leading edge of the sheet and the bottom-left corner. b in the figure above.
For example, the distance is 9.5 mm (0.37").
In the example, the measured skew is -0.8 mm (-0.03").
If the media registration is not optimal, change the value or use another setting depending on how the registration looks.