HP 2566C - Manual (Page 44)

c. Return to step "1."
Continue to a(^ust the thickness setting and run sub-test 15 until
the vertical lines are straight and the best print quality is obtained.
If you are having print quality problems, see “Optimizing Print
Quality” on page 6-14 for information.
Note
When printing in draft mode, tighten the paper thickness adjustment
lever up one additional position.
4. Check overall print quality.
At this point, your printer is set-up to obtain best print quality.
Follow the instructions on page 3-24 to run sub-test 9 and examine
the printed characters.
PREPARING THE PRINTER FOR OPERATION 3-23