Datamax ST-3210 Operator's Manual page 37

Printhead Assembly
Media Sensor
Printhead Latch
Slide
Ticket Stock
Lower the Printhead Assembly and lock the Printhead Latch.
Turn 'On' the printer and load ticket stock; see Section 3.2.
Lower and lock the Access Cover.
To verify the alignment, press the FEED button several times – the
stopping point should be the same for each ticket that is output. Note
that if the Fault Indicator illuminates, the sensor needs to be
repositioned (see Section 5 for a complete listing of possible causes).
S-Class 29