The Casio SPF-40 (left) looks busy compared ûto the simple Citizen Eco-Drive Diver watch (right), but Casio's engineers have made the functions easy to get at, and they work well.

The wrist watch dates back only about a century - and it was first worn chiefly by women, until World War I proved its practicality for men. Until the end of WW II, advances in watch technology consisted chiefly in automating their winding, and adding a few "complications" like calendar and stopwatch functions. After WW II, watch technology languished about a decade, then began to improve at increasing rates.

Six generations can be distinguished from then to the present: 1. Replacement of human power by electronic power, and the rise of the digital display. 2. Addition of alarm, timer, chime, and stopwatch functions, now standard. 3. Addition of memories, sensors, and…