The first 1911 chronographs used Zenith El Primero cal 400 (Ebel cal 134), which oscillated at 36.000 bauds per hour. Rolex used the same movement in Daytona but downgraded the bph to 28.800. Later models (just like BTR) used the Ebel caliber 137. When Ebel started developing their version of this movement, they bought exclusive rights to the movement design from Lemania, with rights given to Ulysse Nardin for the base plate (which UN used in their calendar watches) and to Breguet for use in the Type XX. Ebel then redesigned the winding mechanism and made a few other changes. They started the project in 1991, and the first watches with the new caliber 137 came out in 1995. Every single Ebel Caliber 137, 139, 240, and 288, which all use the same base, was chronometer-certified.