The 45GS series was the second, and final, series to be manufactured by the Daini Seikosha company.
Unlike the contemporary 61GS series from Suwa Seikosha, the model structure and numbering methodology for the 45GS series is both clear and consistent. A total of 19 distinct models were produced, with 18 of them being available for general public sale.
There were just three calibres used for the 45GS series – the 4520A (no complication), the 4522A (with date complication), and the legendary 4580 VFA.
Both 4520A and 4522A calibres were offered in four case variations. Versions of all case designs can be found for sale on this website.
- -7000 cases are highly angular, with sharp well defined contours, edges and corners. Cases were available in both steel and cap gold variants, with the steel versions being available with two different dial finishes – off-white linen textured, and a dark blue matte. The dark blue is sometimes misinterpreted as being black in colour, and – somewhat confusingly – after-market re-finished dials are available in black. (Total of 6 legitimate models across the two calibres.)
- -7010 cases are oval shaped, with brush metal finish. There are two dial variants for these models – one with 36,000 on the dial, and one without (Total of 4 models – two for each calibre, with and without the 36,000 designation on the dial)
- -8000 cases adhere closely to the “Grammar of Design”, and come in both steel and cap gold. (Total of 4 models, two for each calibre)
- -8010 cases are distinguished by being made in solid 18K gold, and finished with a linen-like texture. (Total of 2 models, one for each calibre)
In addition to the above sixteen models, there was also a version of the 4522-8000 in steel that was made for the Toshiba corporation as a commemorative watch given to employees who celebrated 25 years employment with the company.
Finally, there are two VFA models utilising the 4580 calibre. These models can undoubtedly be considered the absolute pinnacle of the entire vintage Grand Seiko era, and either of them would qualify without peer as the ultimate “grail” piece in any vintage Grand Seiko collection – not just because of their rarity, but also because the represent the ultimate achievement of what Grand Seiko was all about – creating quite simply the best watch on the planet.
They are both significantly rarer than the 61GS series VFA’s, with numbers produced of each example – the 4580-7000, and 4580-7010, almost certainly only in the double digits. Just one example of the former, and two examples of the latter, have come to the market in the last 3 years.
In 1968, Seiko submitted 103 specially regulated examples of the 4520 movement to the Neuchatel Observatory in Switzerland for chronometry certification. Of the 103 submitted movements, 73 passed certification and were cased up as Seiko Astronomical Observatory Chronometers.
The following year, Seiko submitted 30 examples of the 4580 movement to Neuchatel, of which 25 passed certification. It is suggested that these movements were also destined for use in the Astronomical Observatory Chronometer, and examples of those watches with this calibre have been identified.
Based on the above, it can be assumed that a total of 98 Astronomical Observatory Chronometers were sold.
Finally in 1970, a further 150 examples of the 4580 movement were submitted, of which 128 passed certification. It is believed that it is these 128 movements that found their way into the 4580-7000 and 4580-7010 watches. If made in roughly the same number, it means that each of these watches is significantly rarer than the Astronomical Observatory Chronometer.
 http://watchesbysjx.com/2013/06/explaining-seikos-legendary-history-in-swiss-chronometer-trials-with-live-pictures-of-its-landmark-astronomical-observatory-chronometer.html , with amendment following discussions with vintage Grand Seiko experts in Japan, awaiting verification from Seiko.