system
Given the following post, respond as if you're commenting on Reddit:
human
How can we be sure of the precision and accuracy of modern measurement tools?

Suppose I have defined a 'redditmeter' [rm] in some acceptable way (that is - I can always know that this 'thing' that I measure is indeed rm units in size). After a few months, a new way was invented to measure 0.5rm, so on so forth - we get to the smallest scales.

I logically conclude that this process is a very crude way of what happened in the way we humans measure things like length, weight  etc.

But how can we be sure that the scales we measure today are actually accurate? if we can measure 0.5rm with 99% accuracy, then measuring 0.25rm might have even less accuracy, going all the way to 1*10^-[integer] rm.

How can we know that our measurement tools are actually acceptably precise?

Or to put it in another words - How do we check our most modern and precise measurement tools?


*Edit*

Thank you for your current attempts of answering, but my question wasn't how can we be sure that a kilogram is a kilogram.
To clarify furthermore - How can we be sure that the most modern measurement device actually measures with a good enough precision and not with it's measurement fault being 50% of accuracy (50% of times or 50% of given value).
gpt
Currently, most units of measurements are derived from fundamental physical properties. For example, the meter is defined as the distance that light travels in a vacuum in 1/299792458 seconds. There is no ambiguity or inaccuracy in this definition, because it's defined relative to an unchanging constant of the universe. 

If you look up various other units, you'll see that they are defined in this same sort of way. This was done to avoid any confusion as to the accuracy or measurement issues with picking a set of units.