Robert Downey Jr. wears a Devon Tread 1F

During the filming of Avengers: Infinity War (2018), Robert Downey Jr. posed for a photo on a tree-lined location set, still half in costume, the housing on his chest showing through a grey training top, with his fist raised toward the lens. On his left wrist sat a rectangular machine with a transparent face, and inside it, black belts printed with large yellow numerals wrapped around visible rollers.

Watch people noticed before the film existed. In July 2017, nearly a year ahead of release, a watch site spotted the device in that set photo, messaged Devon Works through its Facebook page, and got a plain answer back: yes, Robert Downey Jr. would be wearing a Devon Works timepiece. He had borrowed it from the company.

The watch is a Devon Tread 1F, built by Devon Works, an American maker, and it tells time on belts: strips of glass-reinforced nylon carrying bold yellow numerals, driven by micro-step motors, read by optical cells, the whole system run by a microprocessor through 313 electrical contacts. A lithium-polymer battery keeps it alive for about two weeks, after which the watch goes back on a wireless charging tower for roughly twenty hours. When the film came out it retailed for 19,900 dollars.

In the finished cut the watch is a blink, what one watch writer called a fleeting appearance, and the clearest look the public ever got remained that photo from the set. Scott Devon, the founder, said afterward that it had been nerve-wracking not knowing whether the watch survived the final edit, that Downey had been true to his word and made it happen, and that being in the movie was the highlight of his years in watchmaking.