Baume & Mercier caliber BM13-1975 COSC
BM13-1975 COSC description
Caliber BM13-1975A 'Baumatic' is a self-winding movement based on the BM12 movement. Most notable difference is the missing TwinSpir balance spring -made of two layers of silicon due- to patent issues. The present version is COSC-certified; the movement also comes in a non-certified version.