I have a terrible time making accurate HSTs using any kind of ruler.
Am not doing a quilt with lots it HSTs and i'm using Triangles on a Roll paper. I have it in 2, 3, 4, and 5 inch (finished size of triangle).
It's wonderful, easy and my HSTs are no longer wonky. What a relief.
I recommend it. Not too expensive either and tears off like thin foundation paper.