Black Mark Sensors

There are three methods or settings for printers to detect a tag or label length. All thermal printers use sensors or optics that read distances between each gap to determine label or tag length:

Black Mark Sensing

Also referred to as a black mark bars, black mark sensing labels, have lines or bars printed on their liner, or in a specific area of a thermal tag that is used by the printer as a start / stop gap sensing mode. The printer setting is set to black mark and the sensor must pass over an area of solid black, that has no interference with other black copy on the tag or label to confuse start and stop points. This mark is a printed black area, always in the same position either between or on each tag or label.

Gap Marks

Gap marks are typically die cut areas between each label that a printer uses to optically sense the space between each label, to determine start / stop gap sensing. Notches and cut out holes are another method of gap sensing typically used with paper or tags. The sensor on the printer must be aligned to "see" this cut out area. Some printers have center gap readers only, (more common in desk top printers), but most mid-range and industrial printers have an adjustable gap sensor.


Continuous labels, receipt paper and tapes have no gaps. Software often controls the stop and start by distance and the gap sensor is turned off. The printer will simply start printing the first label and print each subsequent label immediately after that previous one.

Gap settings are typically controlled through the print driver or label software settings. Contact your BarcodeFactory technical support to help.

Special Considerations
  • Some labels and tags can require more effort in the initial software or printer set-up and may always require a specific gap sensing method
  • Special Shape labels: Labels that are circular, or multi side will require an adjustable sensor head that must not be moved, to always read a correct gap
  • Clear label material requires a black mark sensor bar on the liner
  • Often a label or tag that has full color bleeding off the top or bottom edges will trick the sensor into thinking that is a black mark sensor. These labels will also need printed marks, lines or gaps to help the printer see the exact gap, or some adjustment to the sensitivity of the head
  • When printing small electronic or jewelry labels registration can become difficult. Black Line sensors are strongly suggested

Remember, printing black mark sensors will add cost to your labels, but your printer may not work without them. We will be happy to review your application and recommend the best and lowest cost method to sense gap and have a productive tag or label print application