I've been making charity quilts about 42 X 54. According to the standard method, they require 3 1/3 yds of backing. Using the Flynn method, I use only 2 yds. Significant savings.
For a visual explanation of the technique, try this link:
Then scroll down to "Diagonal Pieced Back
Click here to print these instructions" and click on the link. There you will get a PDF with drawings that show just how it works. Then I would go back to
to calculate the yardage of fabric needed.
I would just add one caution: because you have created a bias seam, work carefully and avoid tugging or pulling the fabric at any time. My first one wasn't perfect, but practice makes perfect, and my last one (made yesterday) is pretty darn good.
Hope this helps!