With elongation, the lines at the left-hand side (leading edge) of the verification chart are at the correct position. The image is elongated / shrunk at the right-hand side (trailing edge) of the sheet.
Use the X elongation back to adjust the back side.
Use the X elongation front to adjust the front side.
Measure the distance between the vertical lines at the front side and the back side at the top-right corner.
For example, hold the verification chart against the light, or measure the distance between the line and the edge of the sheet on the front side and the back side.
Measure the distance between the vertical lines at the front side and the back side at the bottom-right corner.
Calculate the average value.
For example: 1 mm is 0.48% of 210 mm (0.04" is 0.48% of 8.27").
If the media registration is not optimal, change the value or use another setting depending on how the registration looks.