I used to have a bathroom scale with a single strain gauge that was accurate. Accurate, as in weigh yourself, pick up a 1lb object, weigh yourself again and see an extra pound. That scale had a "lifetime" nonreplaceable battery in it and after 20 years or so, gave up the ghost.

Every scale I've tried since is wildly inaccurate, and they do have brains and they fake it. Step on, get a random weight within a 5lb range of the true weight. Step on repeatedly, even after the scale has timed out and had to be rezeroed, and get that exact weight again. Fake. Every single 4-sensor scale (one in each corner post) that I've tried does this.

I've since found another relatively vintage single strain gauge scale whose battery still works. And I have a mechanical scale in reserve for when it no longer does.