How do you find out how old a Seiko is by the serial numbers?
The serial number indicates the last digit of the year and month made
in the formaty YMxxxx(x) where months go 1-9,O,N,D so a 8N1234 would be
Jan - 1.
Feb - 2.
Mar - 3.
Apr - 4.
May - 5.
Jun - 6.
Jul - 7.
Aug - 8.
Sep - 9.
Oct - 0.
Nov - N.
Dec - D.
To narrow down the decade you might judge by the case number. One tip
for guessing decade is if the serial is 7 digit, it was probably made
'67 or earlier whereas 6 digits would be '68 or later. (late '67 / early
'68 transition to 6 digit serial numbers).
In this case the serial number is 790197. This means the watch was made
in 1967 (the first 7) in September (the number 9). Of course the year
could be 77, 87, 97 or even 2007. This is where knowing the different
model and case styles helps!