The Tissot 26.R 21 watch movement, introduced in 1958, is an automatic movement characterized by its use of beryllium bronze for the bearings and wheels. The date function is incorporated as a module on the 707P. Notably, the movement features the Incastar regulator, which is the only large-scale produced regulator that utilizes a free oscillating hairspring. The end of the hairspring is fixed between two rollers, allowing for adjustment of its length and ensuring no isochronism error due to the gap between the regulator pins. In terms of functionality, the movement offers an automatic winding mechanism, a sweep seconds hand, and a date function that can be set by +/-24 hours.