Avery Dennison Monarch 9855 Operator's Handbook, Maintenance, Service & Parts Manual page 55

Feed/Cut acts as a toggle switch to change the value by 10 or 1.
For example, to make the contrast 50 (from the default of 0), press
Feed/Cut, then press  five times (50).
5. Press Enter/Pause to select either "Yes" or "No" to print a test label and
check the print contrast. Press Enter/Pause.
6. Press Escape/Clear until you see the Main Menu.
We recommend you check the bar code print quality with a bar code verifier.
If you do not have a bar code verifier or scanner, check the bar code
visually. A bar code that is in spec has complete bars, clear spaces, and
small alphanumeric characters look complete. An in spec bar code may not
look as good as one that is too dark, but it has the highest scan rate.
Dark IN SPEC Light
Setting Supply Options 4-21