Would a balance on the moon still read masses correctly?

Yes, a balance on the Moon would still read masses correctly, as balances measure mass, not weight. While the gravitational pull on the Moon is about one-sixth that of Earth, causing objects to weigh less, the balance would still accurately reflect the mass of the objects placed on it. The principle behind the balance relies on the comparison of inertial mass, which remains constant regardless of the gravitational field strength. Thus, the readings would be consistent with the mass of the objects.