That’s also common, in the self-checkout machines. Instead of scanning the barcode you just drop the item on the surface and select it on the screen.

True, I didn’t consider that. I suppose it’s not that expensive to put scales everywhere.

Depends on the state in the US. Almost every state has relatively strict requirements regarding which models of scales may be used for trade (pricing), and some impose taxes and other fees to keep them in operation. Most scales on grocer floors that are accessible to customers (if you can even find them these days) are clearly marked as "not legal for trade" or have a similar disclaimer -- precisely because it would be too expensive to keep carefully calibrated trade-legal scales exposed to the general public.

in nj, scales are inspected by the local Office of Weights and Measures. mis-calibrated scales can result in a fine for the grocer.

I had no idea this was a thing, but I’m glad that it is actually a thing.

Meijer (US megastore retailer that competes against Walmart in the American midwest, though generally has slightly higher prices and higher quality items) has introduced this recently with app-based self-checkout, and it's picking up adoption at a fairly quick pace.

Another huge regional grocer, HEB, does this in Texas with their largest and most upscale stores, and it's been a norm for nearly a decade.