Intermec EasyCoder PC4 Programmer's Reference Manual page 117

Chapter 7 — Commands
Remarks:
102
In addition to the label gap sensor, the printers have a black mark
sensor that determines the top of each form by sensing a
preprinted black mark on the back of the media. The sensor is
located slightly to the right of the center of the media path (as
seen from the front of the printer).
Refer to your printer user's manual for specifications of the size
and location of black marks.
Example 1:
On this tag, the black marks are printed on the perforation in a
203.2 dpi (8 dots/mm) printer:
p = 31 mm (248 dots)
1
p = 7.0 mm (56 dots)
2
p = 0.5 mm (4 dots)
3
p
1
The Q command would be:
Q248,B56+4
ESim for the PC4 and PF8 Printer Programmer's Reference Manual
Perforation
p
2
p
3