Elliot Page wears a Cartier Tank

On the Pont de Bir-Hakeim, the steel bridge over the Seine where Cobb teaches Ariadne to build, Elliot Page's Ariadne raises both hands toward a figure across from her as she learns to reshape the dream. On her raised left wrist is a small rectangular watch, gold case, light dial, brown leather strap. It is a Cartier Tank, and the shape gives it away before any logo could.

The Tank is a study in straight lines, and it comes by that honestly. Louis Cartier drew it in 1917 after watching the new Renault FT tanks cross the Western Front, and the case is built from that image: the two vertical bars that frame the dial, the brancards, stand in for the treads, with the dial set between them like the cabin. Cartier offered the first six for sale in 1919 and they were gone within weeks. The dial carries Roman numerals on a railway-track minute ring, with a small blue sapphire set into the crown. Nearly everything Cartier has made since has been some argument with those proportions.

Ariadne is the architect Cobb hires to design the levels of the dream, and she is also the newcomer the film uses to teach the audience its rules. There is a neat rhyme in a watch built entirely from straight lines and proportion sitting on the wrist of the team's architect, though there is no evidence it was a deliberate choice. What the watch will not give up is exactly which Tank it is. It stays on screen only in glances, gold on a brown strap, and the precise reference that floats around online comes from crowdsourced sites that guess more than they confirm.