Introduced in 1988 as the successor to the CA-50, the CA-53W is the calculator watch — an 8-digit keypad on the wrist alongside standard timekeeping, immortalized by Back to the Future Part II and III. Eighteen small buttons cover arithmetic on a resin case that weighs almost nothing.

Dual-time capability tracks a second timezone, and a 1/100-second stopwatch with split-time memory rounds out functions most people forget a $30 watch can have. A full auto-calendar runs programmed until 2099, and the battery lasts roughly five years before needing a change.