Y por ultimo, espero que te ayude esto Santi, tomo prestado esto de una review:
However, whilst God may not play dice, the Omega Watch Company certainly does. In 1968 it phased out the cal. 321 and replaced it with the cal. 861, another Lemania design. Referring to the picture (left), some of the changes are obvious. Gone is the column wheel, replaced by a cam and shuttle. Gone are the balance screws and Breguet overcoil, replaced by no screws and a flat hairspring. (Omega claimed this enabled the beat frequency to be raised to 21,600, giving better accuracy. Better theoretical resistance to perturbations of the balance maybe, but I'm yet to be convinced about the better "accuracy"...) Gone is the Y-shaped bridge, replaced by one which if you squint at it in the right orientation and use a lot of imagination, looks like a map of Australia. (On second thoughts, that could be a good thing). Gone is the standard index, replaced by a micrometer screw adjuster — actually, that is an improvement. And gone is the neat 1/5 second movement of the sweep second hand — now it's 1/6 second which doesn't fit in with anything. Not so obvious is the extra two jewels added, bringing the total up to 19.
If you look closely at the photo, you will see a white nylon part (the brake) just above the centre chrono wheel. This part was introduced on later 861s and only comes into play when the chrono is stopped after timing an event. It prevents the sweep second hand moving from its stopped position, and releases it when the reset button is pushed. Some pundits have criticised the use of a "plastic" part as a lowering of quality standards by Omega, but in fact it is as good as or even better than the corresponding metal brake, as it is self-lubricating. However, when Omega started fitting a display back to certain models it not only tarted up the finish of the movement with rhodium plating but it also reverted to fitting the metal brake, to overcome any perceptions of 'doing things on the cheap'.
In truth, Omega brought in the 861 because it had fewer parts than the 321 and it was cheaper to produce and service, whilst still providing rugged and reliable timekeeping. In spite of my rant above, it's a good movement (with a few idiosyncrasies). But it's lost that 'vintage' look, and that's what collectors are after.
Se puede ver toda enerita aqui (probablemente ya conocida), todo el merito a su autor, por supuesto: