Hacking (Second Stop)
Hacking is the feature where the second hand stops when you pull the crown out. It lets you sync the watch to another timepiece down to the exact second. Not every mechanical movement has it.
On a watch with hacking, pulling the crown to its outer position stops the second hand; push it back at the right second and the watch starts in perfect sync. This matters to anyone who wants to set the time beyond just the minute. The feature is not a given at this price: Seiko's newer 4R36 and Orient's F6922 both hack, while the older Seiko 7S26 does not. When buying a mechanical watch, it is worth asking whether the movement hacks.