Baume and Mercier, a well known Swiss company that started in 1830 and is still around today. No point in posting their history here when there are plenty of other sites doing that; the company web site is http://www.baume-et-mercier.com
In the 1970’s, they introduced their Tronosonic range which housed the ESA tuning fork movements. They were also one of the few manufacturers to use the ESA chronograph tuning fork movement, ESA 9210.
The standard Tronosonic range housed the ESA 9162 (date only) and ESA 9164 (day and date) movements and, like many watch manufacturers, they assigned their own calibre numbers to these movements. So in my rather nice stainless steel example below, the calibre “BM 19162” is actually the ESA 9162.
When ESA released their chronograph tuning fork movement, ESA 9210, Baume and Mercier were one of the few companies to produce a chronograph tuning fork watch; the other companies being Omega, Longines, Certina and Derby. The ESA 9210 is a fascinating and complex movement and I have devoted a page to it: the ESA 9210 Tuning Fork Chronograph movement.
My example below was in a poor state when I bought it — first four photos below. They are not common, so I bought whatever I could find accepting that It needed quite a lot of work. The movement was wrecked but I had a new-old-stock movement, so that wasn’t a problem. But the case had various issues like a broken crystal, damaged chapter ring and broken pusher. None of these B&M parts are available, but luckily for me, these parts were interchangeable with the Omega Speedsonic, another ESA 9210 based watch.