Casio’s new F-B100W shows how innovation can mean adding exactly enough technology, then stopping. The Casio F-91W is one of those rare products that seems almost immune to progress. It debuted in 1989, when I was a teenager and Taylor Swift was a newborn. Thirty-seven years later, Casio STILL makes it. You can buy a new one for about $20, and it does what it always did: tells time, runs a stopwatch, sounds an alarm and lights up when it’s dark. The battery lasts about seven years. Now Casio...