Hi Steve, I am sure other's here will give you a clearer idea but when doing them myself I try to look at as many close up pics of originals as I can before hand focusing on the bale and strap joining itself. Then match the fold, Tack it with a pin and start the stitch. I know originals were machine done but plenty of originals were re done, Period repaired by hand. I don't think there is an actual regulation on the fold length etc but could be wrong, Like said I just match by eye and it usually turns out okay. Best of luck pal! Can't wait to see this one finished! Cheers, Sean. EDIT. I have attached a pic below similar to what I was describing.