Vintage SEIKO "Time Sonar" 7015A-6010S, ca. 1978 (from Tim)

Seiko must have been very proud of this automatic Chronograph movement 7015A (base 7005)...
otherwise they would not have shown it via this original smoked acrylic back window. Unlike the 6138 and 6139, this is not a genuine chronograph. It is rather a modular chronograph based on the 7005 movement. The second generation of 7005s was produced from 1971 to 1978 and contained amongst other variations the 7015A chronograph above. These chronograph calibers were considered "high-end" calibers.