Complication guide
Hacking seconds and hand-winding: how the complication works
Hacking stops the seconds hand when the crown is pulled out, for setting to a reference; hand-winding lets the crown wind the mainspring directly.
Two small conveniences separate calibers that otherwise look identical. Hacking, or a stop-seconds, brakes the balance the moment the crown is pulled to set the time, so the seconds hand freezes and the watch can be started exactly on a reference. Hand-winding lets the mainspring be wound from the crown rather than only by the rotor.
These features are a common upgrade path. The Seiko 7S26 neither hacks nor hand-winds, while its dimensionally similar successors the NH35 and 4R35 do both, which is exactly why they are a popular drop-in choice when their footprint matches the case.
Related complications and calibers
ChronographA chronograph is a watch with a built-in stopwatch, started, stopped a
Automatic windingAn automatic, or self-winding, movement winds its own mainspring from
Date and day-dateA date complication shows the calendar date through an aperture; a day
GMT and second time zoneA GMT watch shows a second time zone on an extra hand that circles the
Seiko NH35caliber and drop-in group
Seiko 7S26caliber and drop-in group
Seiko 4R35caliber and drop-in group
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