Looking for suggestions of a constant length or time natural phenomenon in order to derive unit conversion.
So here's the scenario:
Guy from Earth wakes up with his mind in robot body. He doesn't know how tall or large it is (can't use previous stride or height as reference) . He is not on Earth (can't use living or astronomical references - AU, day, year, gravity, etc).
He has a local system of units, but wants to convert it in his head to the meters/seconds/etc that he's used to. He's an avid outdoorsman, but has only basic understanding of physical constants.
For example, he knows an AU is about 150,000,000 km, but knows that isn't useful here. He knows the length of a meter is tied to the speed of light, but only knows that is about 300,000 km/s and has no way of measuring seconds specifically. He knows a cubic meter of water masses 1000 kg, but can't measure either.
He is remotely aware of ideas like Plank constants, but couldn't even tell you their name.
Basically an everyday person.
Is there a macroscopic phenomenon that has a consistent size or timing that he could use? I thought about crystal lattices (e.g. basalt pillars), but they're too inconsistent. You have to go nanoscale to get constants like salt and I couldn't come up with a reason for him to know the 0.568 nm constant there.
Any ideas? It's not going to be a monetized work (basically just an idea I couldn't get out of my head) and you will be credited if I can work your suggestion in.