HP DMXTM 400/430 Operator's Manual page 18

Paper/Ribbon
Light:
Ribbon
Switch:
Darkness POT:
8
Getting Started
This light is activated when:
No label and/or ribbon is detected.
The Internal Rewinder (if installed) is not
rotating, (i.e., maximum rewind capacity has
been reached).
For direct-thermal printing, (no ribbon), slide the
switch to the 'off' position. For thermal-transfer
printing, (ribbon installed), slide the switch to the
'on' position.
This POT is used to fine adjust the print darkness
due to variations in different medias and
printheads.
DMX 400/430 Operator's Manual