What are markers and how do they automate glance calculation in eye tracking?

Markers are visually distinguishable patterns (like QR codes) that may be placed in the environment in order to use D-Lab to automatically calculate glances to areas of interest. D-Lab detects the markers by image processing and identifies the size, shape, and position of the markers. These parameters are then used by D-Lab to automatically calculate glances to areas of interest in the environment despite head movement.