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.

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.

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.