This one I had to look up. I had the right idea, but
I didn't consider resetting the stone to the middle each time.
Also,
Tundra could be north as well as south, as can the desert. Two poles and all that. But perhaps some Xanfi lore from the many Xanfi items reveals which. Otherwise trial and error could reveal it.
This puzzle in fact made me
think it wasn't the clue needed for the moving rock. So I went back to the archives where I found the letters and spent a lot of time trying to solve it there somehow, with no luck, hoping that would lead me to the real moving rock clue.