For web/gap media
The printer senses the differences between the label and the liner to determine the print format length.
For continuous roll media
The printer senses only the media’s characteristics.
The print format’s length is set through programming (using a driver or software), or based on the last stored form’s length.
For black mark media
The printer senses the beginning of the mark and the distance to the start of the next black mark to measure the print format length.