The Seiko caliber 6308A, which debuted in 1976, was a very simple, but nevertheless most rugged and reliably constructed selfwindig movement, which is able to run many years without service.
This movement displays hour, minute, second and the current date. The date advances semi-fast and can be corrected in the middle crown position.
The large four-leg balance regulates the pallet-lever movement with 21600 A/h. Of course, it is secured in two Diashock protections to survice all kinds of shocks. The hairspring is connected to a moveable hairspring stud and its effective length is set by the hairspring key without long regulator arm.
The selfwindig mechanism is - typical Seiko - genious and simple: An excenter changer drives the mainspring by only one intermediate gear in both directions. This movement already uses plastic parts in the selfwinding mechanism. This does not only reduce costs, but also eliminates lubrication problems.
Seiko was so confident of the effectiveness of the selfwindig mechanism, that a handwinding mechanism was left out. A little shaking is already sufficient to get it running.
The wheelwork is surprisingly simple, two ruby bearings are only found on the escapement wheel; the directly driven center second and the third wheel use metal bearings on the bridge side, while on the dial side, ruby bearings are used.
An interesting detail is the design of the more or less massive wheels: The minute wheel (second wheel) uses two holes, the third wheel three and the fourth wheel (the directly driven center second) contains four holes. This not only makes the gears lighter as faster they're turning but also allow a simple identification.
On the dial side, most of the space is used by the elaborate date mechanism. At "11" uses a driving wheel made of plastic and contains a moving driver which is responsible for the semi-fast advancing of the date.
At "3:30" you see the quickset wheel, which is effective on the center position of the crown and quickly advances the date by turning the crown. The opposite part of that mechanism can be seen at "2".
Another nice detail is the date spring at "7", which, unlike most of the springs on other manufacturers, does not immideatly fly away when you work on the date mechanism.