Vintage SEIKO 6309-735M R, ca. 1977 (from Tim)
7N1939 is the serial
And from it we know this watch was produced 1977, in November. 1939 is a running production number. With Seiko serial numbers, the decade is never determined. One has to google the history of the watch to be sure about the decade.
There is also a page on my site that deals with Seiko Serial Numbers and their interpretation.