If a marker is untrackable (out of frame, occluded by another marker, blocked by metal, etc) for a series of frames, you can prevent XMALab from trying to track the point in those frames. This is especially useful for tracking from different parts of the sequence, because automatic tracking will not try to track within those frames.

To mark a sequence not to be tracked:

1) Ctrl + Click to select a sequence 2) Ctrl + U to mark the sequence as untrackable

Confirm the dialog that pops up; this will delete the data for the marker and set these frames as untrackable for that marker: