Hell, +/- 1000 pounds would probably be good enough, and even that might be more sensitive than actually needed. A typical shipping container weighs on the order of ~30,000-50,000 pounds (~15,000-25,000 kg). A ship isn't going to sink because a declared-as-40,000 lb container was actually 40,050 lbs. Even if a company loading 1,000 containers systemically mis-declared by 50 lbs and they all got loaded in some asymmetrical way, that'd still only be a 50,000 lbs error, equal to about one shipping container. A modern cargo ship is not going to sink because of an asymmetric load, or an over-load, equal to one shipping container.
If underdeclaring weight became a stability problem sufficient to sink the ship, my guess is that a substantial number of the containers were reporting numbers way off the real values.