Miyota Caliber GM12

Manufacturer	Miyota
Caliber Number	GM12
Movement Type	Quartz, battery-powered
Lignes	10.5”’
Diameter	23.7mm x 22.6mm
Height	2.71mm
Jewel Count	No jewels (0)
Frequency	32,768 Hz
Accuracy Rating	+/- 20 seconds/month
Battery Cell #	SR621SW
Battery Life	3 years
Stem Part #	065-543 (tap 10)
Hand Count	3
Hand Sizes	1.20mm (hrs) / .70mm (mins) / .17mm (secs)
Functions	Central hours; central minutes; central seconds; date at 3:00
Hacking Seconds?	Yes
Country of Manufacture	Made in Japan
Known Models	(Add your watch to the comments below…)

The Miyota caliber GM12 is a quartz movement with a date. This calibre is part of Miyota’s “Slim” line of quartz movements.

In Miyota’s own words:

“Slim movement. Ideal for designs with a thin profile. Multiple variations in size and date display.”

Some of the features of this movement are that it’s hour wheel is already assembled; it is dust proof; the coil is covered to avoid scratching during a battery change; the date adjusting the super quick; and it is easy to assemble on a flat desk.

Similar Calibers:

There is a similar caliber GM02 with the main difference being that the GM12 has a date and the GM02 has a day-date. All other specs appear to be the same.

Interchangeability:

Sometimes this caliber number is confused with a similar cal. “6M12”. The GM12 is considered to be an interchangeable upgrade from the 6M12.

As of this post, the GM12 is part of Miyota’s current catalog, while the 6M12 has been discontinued.

Other potential interchangeable movements: Miyota 0640, Miyota 3W10, Citizen 3810, Citizen 6110, Citizen 6112, Bulova 6362.17.

Replacement Prices:

At the time of this post, replacement prices for the GM12 were found in the range of $4.99 USD to $22.00 USD.

Important Notes About Setting the Date:

According to official technical documentation, Miyota states the following about changing the date:

• Do not set the date when the hands are between the hours of 9:00 PM to 1:00 AM

This is when the date setting mechanism is activated and forcing the calendar forwards could disrupt the system or even break the components.

Additional Resources:

• Official 6M12 tech drawings (pdf)
• Official 6M12 instruction manual (pdf)
• More Miyota mentions