I checked the website on the tool in the picture and found this page:
http://www.thecardladies.com/SimplyPerfectTools.htmIt explains a little bit about this and related tools. It looks like the inner track is actually meant for using the mini rollers, not the larger sized. A regular wheel would be rolled along the outside edge, and then you'd slide the tool along as you wanted to extend the line.
HTH!