The Eterna 1421UD watch movement, produced during the period of 1975-1977, is characterized by having a balance with three spokes instead of the usual two. Additionally, the plate recess for the lever cock is larger compared to its predecessor. Although a mixture of old and new components occurred during the transition period, resulting in incorrect signatures, both the old and new components remain interchangeable. This movement offers automatic winding functionality and includes a sweep second feature.