The easiest way for me to square up the HSTs is to have a square ruler the same size as the completed square should be. Center your ruler (with the 90 angle line on your fabric line) and cut around. It's easy to line up again as you turn -- just use the angle line on the square.

My 4 1/2" ruler is just the right size for HSTs that go into a 12" block using 9 squares. Does that make sense?

I found a way that works for me. I fold the triangle in half and finger press....so a line runs from the point to the middle of the long side. Let's say we're sewing it to a square. i fold the square into fourths and finger press. I lay the triangle on the square, and make sure the folds match up.

Hope this helps.