Datamax ST-3210 Operator's Manual page 21

Standard Media Sensor" using Roll Stock –
"
Mount the roll of ticket stock on the Roll Hanger so that it
unwinds in the direction shown by the arrow in the drawing
below. (The TOF Marks must be wound inward on the roll; see
Section 6 for ticket stock specifications).
Ensure that the Printhead Latch is in the 'Locked' position.
Unlocked
Locked
Roll Hanger
S-Class 13