What's common? Standardisation in the Swiss industry.

Well, you have probably guessed that they are by the same maker and you would be right, they are all by Tavannes, the two on the left were made within a few weeks of each other probably in 1922, the one on the right for Benson in 1936.

But there is a bit more too it than that. By the time these movements were made the Swiss had gone a long way down the path of standardisation. Apart from the obvious differences in the top plate / cock / bridge design and the additional screw holes etc in the face plate to accommodate them, these three movements are, except also for the type and quality of the finish, essentially the same with all of the wheels, the setting mechanism, the balance staffs, etc  interchangeable when new.

The  movement in the centre arrived with a very bent centre wheel caused by someone pressing the barrel against the wheel when taking the barrel out, so rather than trying to straighten it I repaired the movement by taking a centre wheel from a scrapped Benson (Tavannes) from c 1935, like the one on the right, which fitted perfectly and required only a trivial adjustment to the cannon pinion to get it all working. A small worn part in the setting mechanism was also replaced from the same scrapped movement. If only old English movements could be repaired as easily!

The fact that the two left hand movements have serial numbers in excess of 13 million also gives an indication of the scale of manufacture that the Swiss companies were now achieving; in 1925 the Swiss [population c 3.8 million] were making about 19 million watches a year whereas the USA [population c 120 million] were making c 9 million and the English industry was essentially dead.

 Scale and lagging behind in standardisation, two of the reasons why the English watch trade went belly up.