Does your scale lie to you?

I guess almost everyone has a bathroom scale somewhere. I also guess that quite a few people are somewhat nervous if not scared to use theirs (I may or may not be one of them), but that is not the topic here.

These days scales are mostly digital. When you get on the scale, it ponders a while (flashing something on display for several seconds) and then, unerringly, shows you the result. There's something that feels trustworthy about that.

You may try this. Step on your scale several times and take readings. Pretty close to same number every time, right? Even with the cheapes possible scale you can find.

But is it really so?

A friend tried this one time. He got on a scale, and got a reading. Tried again, got same reading. Third time, the same.

Then he told his wife to step on.

And then he tried again himself. This time the reading was off from previous reading by several kilograms.

Curious...

After some more experimenting he determined that the scale was horribly inaccurate, and to cover this it remembered last reading, and if new measurement was relatively close to last one, it showed the previous reading again. Different enough weigh reset this memory and started with new number.

Now, one should not expect cheap(est) bathroom scale to be very accurate anyway. Even in that kind of relatively simple analog-to-digital system, there are many places where errors creep in. Main measurement components, amplification and A/D converter as primary culprits.

And when you are trying to shave every cent from the cost of the scale, these things suffer.

I've said this before, and it's worth repeating here again: Never buy a tool from the very cheapest group (make that from two or three cheapest groups if you're ordering directly from china), as it will be pure junk. Pick one from the next price group up, as it very likely is of much better quality.