I want to include units of measurement In my world that are consistent, like the metric system, not based on the length of some random thing, like a king's foot or something. There's an interaction with someone from Earth trying to explain feet and inches, and someone from the other world being so confused at why we over complicate things, but what is the length of a unit for them, and how is it consistently determined? :/
If it helps, a metre was originally 1/10000000th of the length of a quadrant on the meridian of Paris. Then they made a platin bar of that length to use as a consistent measure. Nowadays it's defined as the way light in vacuum travels in the time it takes light in vacuum to travel 1m, so how it's consistently defined really depends a lot on how advanced science and technology are in your setting. (Source: Wikipedia)
Which means the base unit itself is still kind of arbitrary? It's just that it's easy to convert into different units (cm, mm, km and such.) You can use some geographic or even astronomic distance, or some object that's important to them maybe? And then break it down into some natural constant (if they know those) or a permanent reference (a.k.a. the platin bar method.)
(Also I'll have to admit I chuckled in European at that whole "someone from Earth trying to explain feet and inches, and someone from the other world being so confused at why we over complicate things" XD Me too alien buddy, me too. Wait 'til you hear about the Fahrenheit scale)
I'd make a "base-whatever" unit and then add a name to it. Base-10 is metric and base-12 is empirical, so I decided to explain that and then place a name for it. In my case, peds and dracopeds stood in for metres and kilometres, and then I just used empirical and made a comment about the confusion over units of measure between two countries.
Thanks for the help! I think I'm going when a base 10 type, since it's easier to keep track of… And I know my main unit of measure is a "length", and there are half-lengths and "bits" (10 bits to a length) but now I need to decide how big a length is based on how they would mainly use it…