Datamax ST-3210 Operator's Manual page 27

Ticket Exit
The printed tickets are expelled from this opening.
Darkness Control
The Darkness Control adjusts the contrast of the printing on the tickets:
turning the control clockwise darkens the print, while turning the control
counterclockwise lightens it. Darkness can also be controlled through
software.
Indicators
For a brief period after power-up (about 20 seconds), all three indicators
will remain on while the printer performs internal diagnostics.
POWER:
Turning 'On' the power switch lights this indicator.
FAULT:
During normal operation, this indicator will flash briefly as
the printer receives data from the host system; however, if a
fault is detected this indicator stays on. A fault can have
several different causes; see Section 5 for details.
ON-LINE:
In the on-line mode, this indicator lights to denote that the
printer is ready to accept data. Pressing the PAUSE button
while tickets remain to print causes the indicator to flash
repeatedly. This indicator remains off in the off-line mode.
S-Class 19