Worn by: Michael J. Fox as Marty McFly
Reference: Casio CA-50
Brand: Casio
Time-traveling hero Marty McFly wore Casio's CA-50, popularly known as the Calculator Watch—the perfect accessory for this sci-fi romp from Robert Zemeckis. A touchstone of the digital-driven 1980s, the watch remains a cult classic with retro nerd appeal, its defining feature being the eight-digit calculator function that enables operations right on the tiny LCD screen. With its range of functions including stopwatches, multiple time zones, and alarms in addition to the calculator, this humble Casio anticipated the rise of the smartphone and eventually the smartwatch.

Source: https://teddybaldassarre.com/blogs/brands/movie/references/watches