I found this excellant tute late summer, and changed it a bit to make 6-1/2" blocks.
Instead of using paper (which I hate to remove!) I rough cut my strips about 5-5/1/2" and turned them into 4" wide strips.
After cutting the strips, I sewed them together in the way described in the above mentioned tutorial. I made my strips into 40 or 42 long strips to make the best use of the background fabric.
press the seams one way. I only trimmed on the back if the overlap was lover 1/2
trim to 4 wide.
Cut background fabric into WOF by 3-1/2 wide. Join pieces to either side of the pieced strips. and press.
I used a 6-1/2 ruler. If you watch the markings on where you lay the plastic square, all the blocks will be the same. For example, with theis 6-1/2 block, I lined up the 4 mark at the sides of the top, and the 2-1/2 mark at the bottom of the square. Cut out. sew 4 blocks together to make a 12-1/2 square.
This sample shows four 12-1/2 blocks sewn together