Michael J. Fox wears a Casio CA-50

Robert Zemeckis put a Casio CA-50 on Marty McFly's wrist in Back to the Future (1985), the calculator watch with a tiny keypad built into the face. It was an ordinary choice for the time. Casio sold calculator watches by the million through the early and mid-1980s, and they were standard gear for any teenager who wanted to look equipped. Michael J. Fox wears his throughout the film, including the opening scene in Doc Brown's lab.

That ordinariness is the point. Marty is an average suburban kid, and the Casio is what an average suburban kid wore. When he lands in 1955, the digital watch on his wrist belongs to a future the people around him have not reached. Casio built the CA-50 to do arithmetic on the go, and Back to the Future turned it into one of the most recognizable watches in movie history.