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Comment by atonse | Hacker News Reader

This reminds me of making a trip to a jeweler when I was < 10 years old, and noticing that they had a weighing scale that seemed to be down to decimal points of a gram (which I guess counts when you're weighing gold, etc).

And the numbers kept changing even when the scale was empty. I think I had a whole conversation with my grandpa about why that was happening, and we came up with "probably just variations in air/breeze around the scale causing them to change"

No idea if that's actually what it was, but it's plausible if you're doing sub-gram weighing?

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> No idea if that's actually what it was, but it's plausible if you're doing sub-gram weighing?

Yes, even dust particles landing on the scale can impact the reading, which is why when you're measuring really small things and want to be precise, you usually have a little glass/plastic cube around the entire thing too.

Also frequently used for people who measure drugs for various purposes.

> why when you're measuring really small things and want to be precise, you usually have a little glass/plastic cube around the entire thing too.

These weighing instruments with draft shields are usually called analytical balances: https://en.wikipedia.org/wiki/Analytical_balance

Most likely the op amp (or whatever gain stage) noise. After a certain point, you get thermal noise.

But with such scales, low sample rates and averaging are key.

I have a scale in my kitchen that measures with 0.1g precision, and it doesn't do what you describe (change while you're not touching it). Perhaps technology has advanced since the anecdote you describe? Or maybe my scale is just lying to me.

Hmmm then I bet it was a flaw. Or maybe modern scales have microcontrollers that adjust for this?

This was a scale in a jeweler in India. It might have been in the late 80s or mid-90s. I might be misremembering too. So take my anecdote with a grain of salt.

> Or maybe modern scales have microcontrollers that adjust for this?

This seems likely to me.

> So take my anecdote with a grain of salt.

Oh, come on. Surely the scale wasn't that precise.

Your scale may smooth out the fluctuations automatically.

Mine takes a little while to notice when I'm adding something like a tenth of a gram of yeast to a recipe.

Yeah, I'd guess this is what's happening.

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