The present watch is fitted with the cal. 9162 tuning fork movement, named Eterna Sonic 1550. It was introduced in 1969 and produced by Ebauches SA under license from Bulova, based on Bulova’s Accutron design developed by Max Hetzel.

All attempts to construct an electronic timepiece superior to mechanical timepieces in terms of accuracy had initially failed and Bulova entrusted the engineer Max Hetzel with the development of a very precise electronic timepiece.

Max Hetzel believed that the inclusion of a transistor in the movement would help to increase the precision of the timepiece. Furthermore he replaced the balance with a tuning fork, a small piece of metal consisting of two parallel arms soldered together in a U-shape and extended by a shaft. The tuning fork was placed between two transistors and oscillated at 360 Hz, a significantly higher frequency than that of a classic, mechanical movement.