Meter is not our only measure of length. We also have astronomical units to measure length. In school they taught us that they were different units and that we can speak with more precision about the distance between two stars if we talk in astronomical units.
For a long time there were also a bunch of interesting questions such as whether it makes sense to say that the norm meter in Paris is 1-meter long and whether it stays exactly 1-meter long is it's surface oxidates a bit.
Metal changes it's length at different temperature. That means you need a definition of temperature to define the length of the meter if you define it over the norm meter.
Newton thought that there's was a fixed "temperature of blood". Fahrenheit used "body temperature" as a measuring stick for a specific temperature.
It took a lot of science to find the freezing point and the boiling point of water as the perfect way to norm temperature. If you shape the vessel the right way, it's possible to boil water at 102 degree C, so they needed to specify the right conditions.
I either didn't know or hadn't thought in the context about most of what you say here, thank you.
Yet this (the exact length of a meter) is more-or-less settled, in the sense that very many people use it without significant loss of what they want to convey. This is kind of exactly the thing I'd like to learn about - how unit-variable relationships evolve and come to some 'resting position'. How people first come to think about the matter of a subject, than about the ways to describe it, and finally about the number of a common 'piece' used to measure it.
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.