Its light too.  You've seen people moving things from one suitcase that is too heavy to another to avoid a $50 fee at the counter.  I read airports have huge trash problems with items people throw away to avoid the overweight fees.  With this you will know.  Plus if the scale at the check in counter says you are over, demand they use a different one to verify as those scales are notoriously inaccurate.  And, you can only do that if you know.