The first number represents the year and the second number (or letter) represents the month (1-9 for Jan.-Sept.
Unfortunately the Jayhawk Production Date Calculator (by John Gauch) which is linked to in the Quartzimodo article no longer seems to be available, so we built our own.
Another useful resource we found during our research was The Seiko Manufacture Date Decoder on the Retro Seiko website.
It does not seem to be as well known and we hope that our movement database is more complete and that our instructions are more helpful.
As with any part of Watch Sleuth we encourage people to contact us with suggestions, corrections or any other information that would make our site more useful.
Hi Gang, I spent a few hours rewriting my old code for the Seiko Watch Production Date Calculator, and I think it is slightly better than the original.