chances are the monkeys who balanced them the last time don't know what they're doing.. There should only ever be one group, no point at all having weights in separate places. (although theoretically you could have two groups, one on the inside of the rim and one on the outside if there's a lot of side-to-side imbalance, although it's unusual because we generally don't like to see weights on the outside, so they will mount them part way across the inside face)