Very good looking, great unpolished condition and just serviced Seiko Chronograph Automatic “Vader Helmet” 6139-7100 dated by serial number to November 1976. The unique shaped helmet case looks very similar to the pilot line cases used by Omega in the 1970’s. This watch came from the original owner, it sat in a drawer untouched for many years and only needed cleaning and lubrication which we have done, all parts are original. Photos are magnified and show details not seen by naked eye, the case measures 41 mm across x 45 mm lug to lug and is fit with it’s original steel bracelet.
Here is some useful information I found (thanks watchopenia) regarding dating vintage Seiko watches “first u must know the approximate time frame for that specific model before u can use its serial number to track the manufacturing date.The first number is the year in that decade. The second number is the month… 1 to 9 denotes months of January to September. “0”, “N” and”D” denotes October, November and December respectively. The last four digits represent the running number of production.”