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http://www.whitehousemuseum.org/east-wing/theater.htm

Outside of the Reflet or Carree, collectors are beginning to focus on a later model sometimes referred to link as the Galet or Egg. These have another interesting case shape where a large ovular bezel surrounds a smaller dial. The outer portion is often rendered link in organic materials like onyx, acacia wood, and tortoise shell as well as a matching brushed gold. link Various other shaped watches are available though quite hard to find, many examples being Tank-esque rectangular watches.

Noted field adventurer James Stacey once said "For me a field watch has to be as useful and reliable as possible while also managing to link disappear on wrist when you don't need it." If that's the test link for what makes a good field watch and it's as good as any I've heard link the pilot's-watch-cum-field-watch Mark XX certainly passes.