Yesterday I got my bc24 dovetail jig (yay) and I've read the manual and am ready to cut some dovetails today, but one thing remains unclear to me. Right behind the "window" there is a black plastic block that slides to the left or right along the length of the jig. I cannot find anything about it in the manual and it does not seem to appear in the illustrations. Maybe I missed it?
Anyway, what does this peice do?
Thanks.