A couple of years ago, at the Paducah quilt show, I found "Clearly Perfect Angles", a vinyl template that just clings to your throat plate area. I LOVE IT! You just take your RST squares, position them according to the template, and sew the first side, cut, turn, sew the second side, then cut down the middle. Perfect every time, no marking needed. I love making HST, but don't want to mark. If you search for "clearly perfect angles" you will find several places to order from, but some LQS may carry them. I won't be without one! Plus, I leave it on my machine, because it extends the visual 1/4" seam guide all the way to the front edge of your extension table, I use that instead of masking tape. Smooth, slick, easy on easy off (just clean the back to make it clingy again).