Throughout history we have used units of measure that were defined by arbitrary standards; things that were conveniently around when whichever government needed something measured. “How much tax does Bob pay?” “How about charge by his farm?” “Uh, OK? how big is it?” “About twice as big as John’s” “So charge him for two Jonny-acres then. Next!”

They never translated well; not to other countries, and often not between intellectuals.

Now we do have units of measure, like the second, which have been defined based on absolute constants in the universe. Certain discoveries and technologies made this possible. Regardless when we did finally set absolute values of measure; **when did we obtain the technology needed to create one?**

I think the most important one here is probably the second. But I also think that any other absolute unit could have been used to derive the others, so any absolute measurement would be accepted.

The problem is that I need to back up my alternate history, and need to know what the earliest possible point for this advancement would be.

In my understanding it would likely be 1902 when the Curies found the half-life of radium, which is universally constant. Was there an earlier opportunity?