This calibre does not have a movable stud carrier so, beat error is adjusted by rotating the collet that holds the hairspring to the balance. First, the movement is placed in the vertical position and rotated until the balance is horizontally to the left of the pallet fork – the beat error is measured by the tester.
The movement is rotated until the balance is to the right of the pallet fork and the beat error measured again.
This method uses gravity to determine the direction to rotate the collet and, in this case, as the balance left is the higher value, the collet must be rotated clockwise. The balance is removed and the collet rotated using a tool in the cut-out indicated in red and this will bring the stud clockwise as indicated in green. When re-mounted on the cock, the impulse pin on the underside of the balance will have moved relative to the pallet fork and the beat error is reduced.
The opportunity is taken to add the remaining dial side parts, excluding the hour wheel and the movement is finished.
After a few days running, the uncased movement is checked for performance and any further adjustments made which results in the following. This is a non chronometer watch so the specification only requires tests in three positions, CH (dial up), 9H and 6H and Omega require a maximum of 25 seconds variation across the three. I’ll show the five chronometer positions here as with some adjustments, it’s usually possible to be within that specification for all five.
The results are as below and show CH and CB being very close in terms of amplitude and rate and this is important. The amplitudes are still increasing but fair for this age of watch and the movement not being cased. The five position variation is under 23 seconds so is within the three position specification from Omega. Beat error is now under 0.8 ms at 0.3 ms maximum so, this is all fine.
The dial and hands can now be fitted and the movement re-cased.