I don't know whether to classified this as a square shaped or a tonneau shaped case. When I look at it, it gives me an impression of a military tank.
Yeaaaaaa something like the below.... the indestructible tank......
This is a Seiko Presmatic from January 1970. The production of Presmatic was quite short lived. From the scattered information, the production start from August 1969 till October 1970. A span of well over a year only at Seiko Kameido factory. Therefore, they are relatively rare. The late 1960's and early 70's signified the pinnacle of mechanical watches technology before the market was being flooded by Quartz revolution.
I think I settled this as a tonneau case with a measurement of 38 x 42mm excluding its crown. This watch's dial is labelled as 5146-5020R at the bottom. The dial is linen textile in nature with match-stick hour markers. The baton hour and minute hand are highlighted with black insert at the center. The second hand has a red or faded becomes orange dot near its tip.
This Presmatic has day and date function at 3 o'clock. The day wheel is in dual languages; Kanji and English. The date can be quickset by pushing the hexagonal button framed by the partially-inset crown.
Look at the above photo.... Isn't it look like a tank with the big gun pointing to your direction? This watch has thick acrylic crystal.
The top bit of the case is satin or machine finishing, while the sides are mirror finished.
The stainless steel case back is smooth and flat. In the center is a huge engraving of Seiko wording and Daini symbol. The screw in case back also proudly proclaim the country of origin for the watch with Japan-A.
The 5146A on this watch is a 30 Jewels automatic movement with a manual winding capability. It also has the hacking function. This movement is a hi-beater with an amplitude of 28,800 bph. Although the 5146A is not decorated, the movement's construction is very clean, with excellent functional finish.
Below are Japanese watches reference book's section on Seiko Presmatics.