I just started quilting with diagonal lines and am using a Frixion pen to draw on the lines. I find the center by folding my quilt at a diagonal matching up the corners and gently pressing with and iron to create a crease, from there I draw the lines in my quilts. I haven't used the bar for my walking foot, not sure how much I trust it.
Here is what I do...[ATTACH=CONFIG]313094[/ATTACH]