Target and Aldi don't use a scale. Costco does, but I bet it works better for Costco because they carry much less items so weights are more unique?

HyVee actually removed all self-checkouts. This sucks because they had awesome self-checkouts with conveyor belts.

I bet it works better for Costco because they don't stock any items with weights low enough not to be registered by the scale.

Also, the last time I went to my local Costco, you were no longer permitted to check yourself out at the self-checkouts. They didn't remove them, but they had started using them as cashier-staffed checkouts.