Seiko had five series of electronic movement calibres:

• 3100 : 1969
• 3200 : 1972
• 3300 : 1972
• 3700 : 1971
• 07 : Elnix; 1973

I have examples of some of these:

Series 3300

An unusual movement that had both contacts and a transistor. This movement can often be found in own-brand watches of the large American department stores like Sears (brand: Tradition, Stellaris) and Montgomery Ward (brand: Le Gant). It is also possible to find Seiko branded watches with this movement, but these are very rare and were possible sold only in Japan.

Series 3700

The EL-370 is the most common of the Seiko Electronic waches but, frankly, I find the styling of these two watches a little boring compared to other electric / electronic watches of the period; in fact, Seiko’s calibre 6138 and 6139 chrono automatics from a few years earlier are much more interesting!

Series 070 (Elnix)

The less common Seiko ELNIXs from 1973. They have a frequency of 4 Hz. and feature the 0702 calibre.