The spread of weighing systems across Western Eurasia 4k years ago
archaeologynewsnetwork.blogspot.com
archaeologynewsnetwork.blogspot.com
Something I would like to understand is how these old systems scaled the reference measurements to order of magnitude larger/smaller weights to measure. Up until recently (before the SI redefinition of weight to physical constants) this was an issue even with the modern definition of the kg where for measuring larger and larger weights we essentially have to resort to larger reference weights. And in doing so the manufacturing complexity grows significantly if you want to hold the same uncertainty (as a %). And of course, this applies when measuring masses significantly smaller than the reference 1kg prototype.
Note that many old measurement systems use factors other than 10, which happen to be easy to multiply/divide with ratios of 2 and 3, which happens to be very easy to make levers/beams for.
First, you can put two equal weights on the scale, then swap them to make sure they are the same, AND the scale is fare.
Next, you could make duplicates of that weight. You could then use some small number of them to make a heavier standard.
You could also make some smaller weights, slightly heavier than 1/2 of the weight, and grind them down until they add up to 1 standard unit. You could then work on duplicating the heavier one, and then shave both of them down a bit at a time until they are equal, and match the standard weight.
With time, you could probably come up with a fairly good set of standards, each up/down would be correct to a tolerance of the sensitivity of the scale.
All of this without a modern beam balance.
In the absence of trade there would be no reason for them to stabilise, but with trade there is every incentive for them to do so even over long distances and between people groups who don't know of each others existence.
That force is commerce, and it has almost never been absent in human history.