ETA Caliber A31.111

Manufacturer	ETA
Caliber Number	A31.111, A31111
Movement Type	Automatic, self-winding mechanical
Lignes	11.5”’
Diameter	25.6mm
Height	3.85mm
Jewel Count	21
Beat Rate / Frequency	25,200 vph / 3.5 Hz
Lift Angle	Unconfirmed
Power Reserve	72 hours
Rotor Style	Ball-bearing system
Hand-Windable?	Yes
Anti-Shock Device	Nivashock
Balance Spring	Nivachron
Hand Count	3
Functions	Central hours; central minutes; central sweeping seconds; date at 3:00
Hacking Seconds?	Yes
Country of Manufacture	Switzerland, Swiss made
Known Models	MIDO Ocean Star 39, MIDO Baroncelli Heritage Automatic (Add your watch to the comments below…)

The ETA caliber A31.111 is an automatic 3-hand movement with a date. This caliber appears to be the same as the ETA A31.L11, but used exclusively in Mido watches (if you find it used in other brands, please comment below). To add even more caliber confusion, when Mido uses it, they call it their caliber 72.

Base Movement:

The A31.111 is based on the ETA 2892-A2 framework, and is a result of the post unavailable-to-brands-outside-of-Swatch-Group era of ETA movements.

When ETA stopped supplying movements to brands outside of their parent conglomerate’s portfolio, some changes were made to existing calibers (such as extended power reserve, use of Swatch Group’s proprietary anti-shock device, beat rate lowered to help with the increased power reserve, removed regulator to make it harder for watch owners to adjust the timing of their own watch) and the caliber numbers were changed. This new generation of movements are only produced for brands within Swatch Group. Technical documentation is also not available for these calibres.

Many of the MIDO watches with the A31.111 have a solid caseback with no view into the movement, however, the Baroncelli Heritage Gent does offer transparency into the watch. At the time of this post, MIDO’s catalog still pictured a model with the ETA 2892A2, making it possible to do a side-by-side to display the visible differences between the two calibers:

Additional Resources:

• MIDO user manual (pdf)