I use a ruler that has the 1/4" mark, put this line diagonally across the block from top to bottom and draw a line. I turn it around and do the same thing on the opposite side eliminating the middle mark from corner to corner. One less step, one less mark. At the same time you can see that these marks are exactly 1/2" apart.
I use a slightly used paper nail file. The nail file holds the fabric in place without stretching the fabric as you pull the pen across the diagonal. If the file is slightly used there is no chance of damaging fine fabrics. Then of course I sew at a 1/4 inch away from the line and cut on the line.
Marie , I use a rule also that has the 1/4 in line on it .I love mine ..Barbara
EAT!! SLEEP !! QUILT!!