Epson Stylus pro 7900 Repair Manual page 340

Pro 7900 and 9900 Field Repair Guide 10/6/10
7. This adjustment pattern will be printed.
Paper Feed Direction
This is what a good pattern looks like.
Slight overlap
Slight underlap
Slight underlap
Each of these 3 lines are equal distant from the top to the bottom. Compare each line to itself, not to each other.
Printer Component, Software Item, LCD Display, Printer Button
PF Slant Adjustment Page 340.