Interesting. I used those IGFA calcs on two of my fish and one was near dead on and the other was off by a pound. I guess in the end only a certified scale is the most guaranteed way to tell the truth. I think ultimately length is more accurate to correct weight than girth is. I have a friend who stick big pigs all spring and he has an adhesive tape measure on the lip of the boat. Everytime he catches one and it measures 24 inches long, he says it's a ten. I've said he was full of it countless times and weighed the fish and guess what, every time he was right. He said a 22 is almost always an eight. Conversely an 11.2 I caught was 24 inches long while a 26 I caught was 15. I caught a spawned out 23 incher that only weighed 6.7 pounds once. So anything is possible. Again I think the certified scale is the most accurate means of knowing the truth about each fish.