You can adjust the shuttle carrier so it is closer or farther away from the race, and maybe that is what they are talking about. I'm in the office so can't go dig up any of my manuals until I get home this evening. I would not be surprised to find there is an adjustment to affect the total travel of the shuttle. Some machines have a bit of a "hitch" in movement too, not sure what it does, but it's interesting to note.