So when you read that a watch like the Seiko Diver Automatic Orange has a 40-hour power reserve, that doesn’t necessarily mean you can leave it for almost two days without having to reset it. The maximum TOWBND (Time Off-Wrist But Not Dead) depends on how much PR is left. How much power reserve is enough?
On average, most automatic watches have a power reserve of between 36 and 42 hours, some even 50 or 70 hours, meaning that the watch can run for that duration on a full wind. How Much Power Reserve Do You Need?
What Is The Power Reserve On A Watch? To put it simply, a power reserve is a feature found on an automatic (mechanical) watch that refers to the amount of time the watch will run after it’s fully wound. In other words, it is the available energy stored in a watch's mainspring, and once the power reserve has run out, your watch will stop.
The longer the power reserve, the longer you can leave your watch between wearing or winding – regardless of how much power reserve is left when you leave it. How much PR you “need” depends on a) whether you give a damn and b) your watch wearing habits. Generally speaking, most mechanical watches have a power reserve between 40 and 50 hours.
Damn you Seiko Spring Drive! If you want to leave your automatic (self-winding) watch for a full weekend or longer, pop it on a watch winder. Not only does a winder maintain the time/date/etc. for as long as it’s on, it helps preserve your watch’s health (as with any mechanical device, regular use keeps the bits from seizing-up).
It is recommended that you observe the power reserve indicator to check the level of remaining power of your watch. In a case where you wear the watch for a short period of time each day, observe the power reserve indicator to check the level of the remaining power. If necessary, manually wind the mainspring.