Well after many disappointing tries at HST, I have found the most successful way, for me , is to cut the squares bigger. On a quilt I am making now, using squares that are 3 1/2" in a ninepatch, I am cutting 4" squares for the HST, because my eyes get strained looking for the 7/8 mark and I see that measurement as pretty irrelevent--I just go to the next most easy recognized measurement and don't care too much about losing an eighth of an inch of fabric. I draw a diagonal line down the middle of the two four inch squares that are placed right sides together, stitch a scant 1/4 on each side of the line, cut apart, press open and then square it down to 3 1/2" using the diagonal line on my 6 1/2" ruler to square it up.