90% of the time I use a straight edge ruler that is 2" X 10" which is etched with 1/4" lines going lengthwise along the ruler and lines across the ruler at 1" intervals and naturally at a 90° angle (perpendicular to) to the edge you place your hopping foot along. I use the lines which run perpendicular to check myself to make sure I am staying square to the line I just stitched for example, if you were making a square. It keeps me straight. I use the marks that run the length of the ruler at 1/4" intervals as a check to ruler placement as well against the line I just stitched or previous lines in a succession. Having said all that, if you are familiar with Judi Madsen, she says she always pre marks her lines, because that is the only way you can be sure they will end up where you want them. I've done it both ways, marked and unmarked, and I always end up with better results when I premark my lines. Stitching on an angle always throws me. With practice you will get better an eyeballing where your ruler needs to be at the other end to hit your mark. Even with marked lines, I always put my needle down in the line I'm about to stitch, and then look down the length of the ruler to see if it's running square with your marked line or other reference point. It'll get better, it just takes some practice and it helps to have some reference lines etched or drawn on your ruler. I've used this same ruler on my Janome 6600, my Sweet 16 Sitdown and now my APQS Lenni. It's my favourite all round. Not to big to hold onto, but big enough to go a fair distance. Once you get the hang of it, you won't be able to do without it!