First off, welcome aboard pat. This is a great site full of great people with a wealth of information to be shared by all.
Their are a couple options I would try, 1) take your bow to a local bow shop and have them check it on their scale, I doubt they would charge anything. 2) if you have a digital bathroom scale you could weight yourself first and then hold something approximately 20-30 lbs and subtract the difference between the two. Then suspend that weight from your scale to see if your scale is the same.
Wes