Started As Frères Baume in 1830 in Geneva, by brothers Louis-Victor and Célestin Baume, the manufacturer afterwards partnered with Paul Mercier in 1918, turning out to be the Baume & Mercier we know today. For the duration of a particularly demanding time period for that brand, Baume & Mercier joined https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/