The Certina 25-65M watch movement, used from 1958 onwards, incorporates several notable features. The winding gear is constructed with beryllium bronze, enhancing its durability. A distinctive characteristic of this movement is the Incastar regulator, which is the first widely produced regulator to include a free oscillating hairspring. The hairspring's end is fixed between two rollers, allowing for length adjustment without isochronism errors caused by the gap between the regulator pins. Additionally, the Certina 25-65M movement is the smallest diameter for a serial automatic movement that includes a sweep second function.