The only difference between the 3/4 stitch symbol and the 1/4 stitch symbol is that the square around the 1/4 stitch symbol, therefore it is easy to get them mixed up. The 1/2 stitch symbol is hard to see if you have a different color floss 1/4 stitch in the corner where the 1/2 stitch symbol is or a back stitch across the 1/2 stitch. Because of these problems I am having, I would suggest the following changes: make the 1/2 stitch with two 1/4 stitch symbols in opposite corners with no square around the symbols and a line from one corner to the other through the symbols; make the 3/4 stitch with a 1/4 stitch and a 1/2 stitch symbols. I hope you will make these changes.