Shed Measures
Hey Warren, in defense of absolutneil, I too measure the length of the shed skins to measure my corns. Why? I think it is the closest I'll get to being 'accurate.' If one really wanted accuracy, then they would have to either kill the snake, or sedate it, then measure, otherwise it will have to be a 'best guess.' I have measured snakes while they've been on-the-run in all sorts of situations, both outdoors and indoors, never are they completely straightened out for an accurate measure to be made. I have found that measuring the skins has--for the most part--confirmed my best guesses, however. In other words, I've gotten the same, or very close to the same, readings whether I measured the skin or the squirming snake. Measuring the skin is much easier and quicker for my schedule and, to me, seems to be as accurate as I'm going to get.
In defense of your position, I understand what you are saying about the lack of accuracy in measuring sheds. To add to your argument, a lot of times, sheds aren't 'good,' or are good, but are broken, and one is left trying to manage more than one piece.
It is by no means an approach which assures absolute accuracy, but, as long as I'm in the ballpark, and I know that it's only a best guess and nothing more, then that's good enough for me.
To sate my need for accuracy, I use a gram scale to measure my corns' weight gain. It's a little bit easier to close up a corn in a cup, box, or pillow case, and weigh it, than it is to mess with a corn snake in one hand and a measuring tape in the other.