Occasionally, it's nice to wear a high-quality vintage watch. It tells the time and nothing else. So any activities to do with time required some mental effort, maybe even a little mental arithmetic in the form of base 60 addition or subtraction. Such effort is good exercise for the mind, thereby keeping it in good condition.
The other day, I was wearing this beautiful watch:
(more pictures here).
Suddenly, my dear wife wanted to be reminded of something in 55 minutes' time. Without thinking. I rushed to my collection, strapped this one on and set the count-down timer accordingly. Didn't even have to think about it. 55 minutes later, sure enough it beeped. "Why is this watch beeping?", I asked. Duh!
(see more tool watches here).
When I think back to my youth, "55 minutes" was about an hour, something easily handled by the mind and confirmed by a couple of glances at the Elgin or whatever. The seconds hand's main duty was to confirm that your watch was running. At school, we learned our multiplication tables by rote up to 12x and we also learned how to do long division on the back of a fag packet. Those were the days when shopkeepers and counter clerks added up long columns of figures on sales receipts and general ledgers with nary a calculator in sight. Discounts or markups were figured mentally.
I would say that progress in the tools of mankind, not just watches, has reduced our mental agility quite considerably. What say you?