The ETA 9157 is an electronic tuning fork watch movement developed by ETA (under Ebauches SA, or ESA) in the late 1960s, marking a transitional technology between mechanical and quartz eras. Introduced around 1968 and produced into the 1970s, it powered affordable electronic watches with reliable timekeeping via an electronically controlled balance.
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Key Features

Tuning Fork Mechanism: Operates at 28,800 A/h (vibrations per hour) with a sweep seconds hand for smooth motion, using a balance motor rather than a traditional escapement.

Dimensions and Jewels: Measures 13 lignes (29mm diameter) in third-generation versions, featuring seven jewels for reduced friction.

Functions: Includes day/date display with quickset date (via 18-24 hour adjustment) and mechanical hacking seconds for precise synchronization.

Power Source: Battery-powered with electronic components like resistors, transistors, and a modern battery placement in later models.
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Historical Context

Part of the ESA Dynotron family (evolving from Cal. 9150 in 1967), the 9157 represented a redesign by 1975, relocating the balance 90 degrees and minimizing electronics for efficiency. It succeeded electric movements like Landeron 4750 but preceded dominant quartz calibers. Production ended by the late 1970s amid quartz dominance.

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