A movement drawn as an X, with nothing in front of it.

An automatic movement carries a rotor, a half-disc of metal that swings over the back of the calibre, and on a skeleton watch that rotor covers the view from one side. Ulysse Nardin built the UN-371 without one: you wind it by the crown, it holds about four days, and both faces of the movement stay clear. The X of bridges is not decoration; it is what holds the wheels in place once the plates are cut away.

The silicon parts are the other reason it works as a daily watch. Ulysse Nardin was the first to put silicon in a series-production movement, in 2001, and the Skeleton X uses it for the escapement and the balance spring, so the exposed mechanism does not care about magnets. In titanium with the blue frame the watch is light for its size and the blue is the only colour on it.

This is a regular Amazon listing from an independent dealer, Luxor Watches on the day we read it, with Amazon’s 30-day return window; it is not a Luxury Stores pre-owned unit. The second button opens the live search for Skeleton Xs in case this one has sold.

Ulysse Nardin skeletons have resold for well under new and close to what pre-owned buyers paid, sometimes more, sometimes less; that is a pattern, not a promise, and nothing here is investment advice.