The Zenith 661 watch movement, developed jointly by Hamilton-Buren, Breitling, and Heuer in 1969, features the Dubois-Depraz 8510 module on the Buren 1281 base. It incorporates a crown positioned at 9 o'clock, a micro rotor for automatic winding, and a double excenter regulator for curb pins and stud carrier. Functionally, the movement enables an automatic chronograph with 60-second, 30-minute, and 12-hour time recording, which is cam switched. Additionally, it includes a date function that can be adjusted by changing the 21-24-hour setting. The Zenith 661 movement has been in use since 1969.