The ref  396.0840 (with metal bracelet) or 196.0054 (on leather strap) houses the cal 1310 movement,  the first analog quartz movement produced by Omega. This watch was introduced in 1975 and is quite unique with its octagonal design. It measures 40mmX42mm and is almost 12mm thick. When these watches came out they were priced quite highly. In 1975 the MSRP for this watch was 1000 CHF (or about 400 US$), which would be equivalent to about 1600US$ today (Using CPI).

Another interesting story is that, as a publicity stunt, Omega apparently strapped 3 of these watches to an arctic research vessel for 3 months and they remained spot on..... This story still needs some verification...:-))