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; one of the best is here. 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, the ESA 9162 (date only) and ESA 9164 (day and date) 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.

Baume and Mercier Tronosonic; All Stainless Steel; 38mm diameter incl. crown; BM 19162 (ESA 9162); 1971

BM 19162 (ESA 9162)

Baume and Mercier Tronosonic; All Stainless Steel; 38mm diameter incl. crown; BM 19162 (ESA 9162); 1971

Inside of screw down case back

Baume and Mercier Tronosonic