Just make the weight you sign up for or move up to the next weight. By, the way Nix I have 3 boys and we've been involved in wrestling for 8 years and none of my boys have ever showed up at a weigh-in over weight. Depending on travel time to tournaments my boys have either weighed the same as we did at home or 2 to 3 tenths lower. So, there's not much difference in the scales. Just by a good dependable scale and you don't have to worry. At Tanita.com they have some very nice scales. They have a wide variety fo scales and a very good price range. Just pick the one that fits your income. We picked one that was around midrange between all the scales. And it has been very accurrate. You said your son has weighed in under 40lbs all year then why was he wrestling 43lbs at Great Bend?