Well the differences between all the versions are quite extensive...to list a few:
Changes in beat rate as has been noted, then changes to the pallet fork bridge (beefing it up after version A), changing the length of the mainsprings (A and C use the same, but B has it's own, and D is also different from all the others), changing from straight to conical pivots on some parts for the C and D, changes in material of the intermediate escape wheel (and number of pinion leaves on this wheel also), even a change in how much you turn the adjustable masses on the balance wheel to make a given change in timing.
And finally change from 2 level design used in the A, B, and C, to the 3 level used in the D, which is the most important thing IMO.
The only way to know for certain is to look at the movement, and the version will be written on the movement plate. Some people have said there is a change in the font on the date wheel also, but I have not verified this information personally. The technical guide for the movement says A, B, and D all use the same date wheel part number, so the change in font is likely due to a change in supplier than anything else, so I would not say 100% that the font will tell you what movement you have.
If you PM me the serial number of your watch, I can look it up on the Omega Extranet and see if it specifies the exact version of the movement in your watch - sometimes it does and sometimes not.
Cheers, Al
Click to expand...