Dell 2135cn Color Laser Printer - Manual (Page 180)

Slow Scan
On the Chart 2 of the color registration chart, find the medium line within the range of white area for each color pattern (Y, M, and C). If you find the medium
line, make a note of the value (-9 - +9) indicated by the medium line for each color.
When the value is 0 for each color, you do not need to adjust the color registration for the slow scan.
When the value is not 0, enter the value using the procedure in "Entering Values" .