The X8 / Cosmotron electro-mechanical movements first produced in 1966 were, for a short time, Citizen’s most accurate watches – capable of reaching chronometer grade standards. They had a very limited life though, since quartz technology was developed soon after and by the mid-1970s they were obsolete.
The most sophisticated Cosmotron was the 7803A – with a 36,000 beat per hour speed they had an additional feature, indicated by a button at the 8 o’clock position. Known as the ‘special’, this button not only zeros the second hand (to 12 o’clock) but also zeros the minute hand when it is within + or – 3 minutes of 12 o’clock. Currently I’m not aware of any other manufacturer that has employed this feature, which I believe is to allow exact synchronisation of the watch. Also, when the button is held in, the second hand is kept at 12 o’clock until the button is released. If the button is pressed and released the hand is zero’d and immediately restarts, as is found in a ‘fly-back‘ chronograph. Citizen also tells us that the Cosmotron Special is capable of chronometer grade accuracy.
Here’s a video of the button in action: http://s282.beta.photobucket.com/user/Sweephand/media/Cosmotron%20Page/7803Hacking.mp4.html
The movement itself is differentiated from other versions by the gold plated finish:
I really like the Cosmotrons – in good condition they are a very accurate timepiece and the hybrid technology they utilise is pretty cool, in my opinion ;)