Spring Drive is a unique watch technology.
It generates energy like every other mechanical watch but combines this with an electronic regulator to deliver a level of precision that no mechanical watch can match.
Specified to one second accuracy per day, the movement uses a conventional gear train as in traditional mechanical watches, but rather than an escapement and balance wheel, instead features Seiko’s Tri-synchro Regulator system in which power delivery to the watch hands is regulated based on a reference quartz signal.
The Spring Drive uses a conventional mainspring and barrel along with automatic and/or stem winding to store energy, just as in a mechanical watch. However, the escapement and balance wheel in mechanical watches is replaced by Seiko’s Tri-synchro Regulator system, a phase-locked loop wherein a rotor, which Seiko refers to as a “glide wheel,” is powered by the mainspring barrel via a stator. The glide wheel in turn powers a reference quartz crystal and accompanying integrated circuit which controls an electromagnetic brake which then regulates the rotational speed of the glide wheel itself.
Seiko’s most accurate current Spring Drive movement promises +/- 0.5 seconds deviation per day (or +/- 10 seconds per month). That’s better than many standard, battery-powered quartz movements and far more accurate than, say, a mechanical chronometer watch that’s certified to be accurate within -4 to +6 seconds per day.