The Seiko 7S26B watch movement is an automatic movement that was introduced in 1957. It incorporates bearings and wheels made of beryllium bronze, which enhances the durability and precision of the timepiece. Notably, the movement features an Incastar regulator, which is the only large-scale produced regulator to utilize a free oscillating hairspring. This unique design ensures accurate timekeeping as the end of the spring is fixed between two rollers, allowing for adjustments to its length. Thus, there is no isochronism error caused by the gap between the regulator pins. Additionally, the Seiko 7S26B movement includes the functions of a sweep second hand and automatic winding.