Welcome to Further Details, a series dedicated to ubiquitous but overlooked elements hidden on your favorite products. This week: the reason your watch's seconds hand stops when setting the time.
The mission has been meticulously choreographed — each soldier knows his or her role and the last thing to do is to synchronize watches before going into action.
This scene is familiar to most of us from films and TV. Unbeknownst to most watch wearers, however, this exact scenario played a part in why their watches have a certain overlooked feature today.
It's now so common and basic, in fact, that it hardly seems like a "feature:" If you've ever set a wristwatch, perhaps you waited for the seconds hand to reach 12 o'clock before pulling out the crown to stop it. That ability to stop the seconds hand is called "hacking." Common, yes, but it's not totally ubiquitous even today, and historically, even less so.
Hacking, or "stop seconds," became more widespread when it was requested by militaries for watches like the A-11 during WWII. Personnel were often not able to be in direct communication but needed to coordinate military actions more precisely than ever. A large central seconds hand that could be stopped and synchronized exactly was mission-critical.
Though it seems simple, the hacking function requires components and engineering that a non-hacking watch doesn't: for the seconds hand to stop, the movement itself needs to be stopped. This is achieved via a lever or brake against the balance wheel itself (the oscillating wheel often visible through a watch's case back that regulates timekeeping) when the crown is pulled into its time-setting position. Pushing the crown back in like a button releases the balance and starts the movement again.
Though most people don't need to plan anything in their lives down to the second, the majority of mechanical watch movements today feature hacking — it's something watch owners have come to expect in all but the most basic and inexpensive watches. It's not just the association with more expensive movements that makes hacking desirable, however: it's simply more satisfying and reassuring to set a watch precisely and to see the minute hand line up with an index as the seconds hand passes 12 — rather than have some approximate representation of the exact time on your wrist.
However, not all watches made today offer hacking, though non-hacking watches are becoming less common. Basic and inexpensive movements such as the Miyota 8215 found in modern watches like, say, the Timex Marlin Automatic don't offer hacking. Swatch's Sistem51 is another example of a non-hacking mechanical movement.
For certain non-hacking watches, however, there is a way to stop the seconds hand — a hack, if you will, in a different sense: (This works with movements like the Seiko 7S26 found in popular models like the Seiko 5 SNK field watch and SKX dive watch — current-production Seiko watches including the Seiko 5 Sports line use newer movements that do hack.) With the crown in time-setting position, turn it slowly so that the hands move ever so slightly counterclockwise. This is called "back hacking" and it should stop the seconds hand. Setting the hands counterclockwise is generally not recommended for a watch's health, but hey — the mission comes first.