Epson AcuLaser C9100 Reference Manual page 350

Left Offset
Makes fine adjustments to the horizontal printing position of the
page. This is useful for fine adjustments.
Caution:
c
Make sure that the printed image does not extend beyond the edge
of the paper. Otherwise, you may damage the printer.
T Offset B
Adjusts the vertical printing position on the back of the paper
when printing on both sides. Use this if the printout on the back
is not where you expected.
L Offset B
Adjusts the horizontal printing position on the back of the paper
when printing on both sides. Use this if the printout on the back
is not where you expected.
350
Functions of the Control Panel