Question about measuring

I followed the measuring instructions on this website and got about 6”BPEL with a rigid ruler, but my willy has a prominent upward curve and if I use a fabric tape and follow it around the curve, it measures about half an inch bigger. I guess it won’t matter in the long run, gains are gains as long as I measure using the same method consistently, I was just wondering if anybody else has encountered this as well?

I also have an upward curve but I can’t get a half inch out of it. Good for you.