A Seiko watch serial number indicates the production date and production number of the watch. In a standard six-digit serial code, the first digit represents the production year, the second digit represents the production month, and the remaining four digits represent the production number.
Seiko watches manufactured before the late 1960s have seven-digit serial codes. The first number of the code denotes only the year in the decade of production, not the exact year. For example, watches from 1969, 1979, and 1989 all have serial numbers that begin with the number nine. Seiko serial numbers display months as a digit from zero to nine or as the letters "O," "N" or "D," which represent the months October, November and December.