Onebyone - I understand what you are staying, but when I go to the diagonal method I am usually desperaate and I have backing pieces that are close to the right size but are small so I do the calculations (I now use one of the online calculators but have been doing this so long that I started when I had to calculate using the formula by hand). By calculating, I can figure out which piece to use that will waste the least amount of fabric.
In order to minimize the bias stretchhing, I starch the fabric when I iron it to make it more stable.