if you've got a bathroom scale weigh yourself without them and then hold one under each arm and weigh the total and subtract original weight, repeat 9 more times, and average the ten readings by shoving the decimel point.....those scales are terrible in the low range, but by doing it this way and averaging, you're using a more accurate range and compensating for scale (ooh, bad pun!) reading inaccuracies.
you'll get a pretty good idea of what a good scale will tell you for anything over, say, 5 or 10 pounds.
this is based on instinct, a little experience, gut feelings and very little real knowledge of the issues involved . . .
. . . so your mileage may vary!
jt ™. .