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Amazing! Can you give us some insight on how that complication functions?
Thanks! There's an aneroid barometer inside, connected to that red needle. The outer bezel is used as an altimeter, with 1=100 feet, so that "100" means 10,000 feet (this is the English-system bezel; there is also a metric one that goes up to 30 (3,000m)). When hiking (or flying your triplane), you set the bezel altitude to the barometer needle at a known altitude, and then, barring major changes in the weather, you have an altimeter.
More here:
http://orologi.forumfree.it/?t=66254963#entry537137295
...and here:
https://omegaforums.net/threads/favre-leuba-bivouac-calibrating-the-barometer.25459/