Could someone tell me how to determine what a scant 1/4 inch is? Ive been trying to make the two color triangles and I have tried the method of measuring the line thru the center of of top square and then drawing line on either side exactly 1/4 inch and I still cant get the a perfect square when cut apart.

You can make your beginning squares slightly larger and then square up your finished half square triangle if you can't get the perfect seam allowance.

I have the best result doing this, but if I really want to do it right and not square up after, I mark down the center of the diagonal, mark 1/4 inch either side then sew just inside the line, not right on it. this allows for the thickness of the fold and any thickness taken up by the size of your pencil when marking. Gee, after saying all that, no wonder I cut bigger then square up! :!:

This is how I do it, too.

From our tutorials section:
Seams
http://www.quiltingboard.com/t-89997-1.htm
http://www.quiltingboard.com/t-122374-1.htm
http://www.quiltingboard.com/t-150279-1.htm

I can't either. I make the square bigger then when I cut in the middle on the diagonal, then press open I trim up the square to be the size I want. It is the only way I have found to get a perfect square.

You don't need any other lines than the one in the middle. Then sew down each side of that line, with your 1/4" foot covering the line when sewing on each side. This gives you a generous HST.