How did we keep rulers standardized?

Question

Is there like a master ruler? Who decided what a length a cm, mm and inch would be and why?

In: Other

Answer 1

There are still physical meters and physical gram standards. These are measured against the physical constants that define the unit of measure. Then another physical standard is measured against the first physical standard. That second physical standard may then be distributed to a calibration lab, who will then compare your instrumentation, perhaps a caliber or a load cell, against that second physical standard. Through this entire chain, data is kept about the comparisons between each standard, all the way back to the original constant. Each link in the chain introduces a small amount of measurement uncertainty that adds up.