Vintage Seiko Seikomatic Weekdater buyer's guide

The Weekdater was built as a practical mid-century automatic rather than a plain dress watch. Its day and date indications put weekday information on the dial, while applied indices and a silver sunburst finish kept the presentation formal. On 6206-8990 examples, the day display at six preserves vertical balance and gives the model its most recognisable face.

Case size changes the character less than case material. The handled examples measure 36 or 37 mm excluding the crown, enough to make the separated calendar display readable without turning the watch into a modern-sized object. Steel suits regular wear better; gold-plated cases demand more caution around exposed edges and lugs.

The main choice is between caliber 6206A and caliber 6218B. The 6206-8990 pairs the 26-jewel 6206A with a day display at six, while the 6218-8950 uses the 35-jewel 6218B and places its full day display at three. These are distinct configurations, not interchangeable variations, so a dial and movement mismatch is a franken warning.

Value sits first in the dial, then in the case. A clean silver sunburst surface with crisp print carries a stronger premium than extra jewels beneath a spotted or refinished dial. Between a sharp steel 6206-8990 and a plated 6218-8950 with comparable mechanics, take the steel watch unless the latter has the materially better dial.

Dial spotting is the first disclosed fault to price, and it ranges from light marks to visible patches across the sunburst surface. A redial is worse: the refinished surface removes the original finish and changes the watch more substantially than ordinary case wear. A genuine service dial is different from a redial, but no supplied example establishes a service-dial specification for this model.

Gold plating wears through at exposed case edges, polishing softens defined case lines, and replacement crowns can alter the recessed profile seen on the 6218-8950. Calendar parts also need to agree with the correct dial layout and caliber. Service history is unknown unless paperwork accompanies the individual watch, so movement condition should never be inferred from a clean exterior.