Rose Marie

I always use Eleanor Burns methods.
For 2 1/2 in half square triangles use two six inch sqs, add two inchs for each size up.
Draw an x and sew 1/4 in down both sides of lines.
Cut in half both ways then on the lines. This gives you 8 triangles at a time. They will be slightly large so you need to square them up.
The best way is with her triangle square up ruler that you only make one cut to square up.
Also if you have a sewing straight line problem, I use the half inch rulers by Fons and Porter to draw my lines with.