Yema Caliber CMM.20

Brand	Yema
Caliber Number	CMM.20
In-House?	(See below…)
Movement Type	Micro-rotor automatic, self-winding mechanical
Diameter	32.2mm
Height	3.7mm
Jewel Count	33 jewels
Parts Count	190 components
Beat Rate / Frequency	28,800 bph / 4 Hz
Accuracy Rating	-3/+7 seconds/day
Lift Angle	51 degrees
Power Reserve	70 hours (+/-10%)
Rotor Style	Micro-rotor made from tungsten
Rotor Winding Direction	Bi-directional
Hand-Windable?	Yes
Manual Winding Direction	Clockwise
Balance Wheel	Glucydur
Anti-Shock Device	Incabloc
Regulator	ETACHRON
Hand Count	3
Functions	Central hours; central minutes; central seconds
Hacking Seconds?	No (see the comments section below for more info)
Finishing	Galvanic treatment
Country of Manufacture	Morteau, France and La Chaux-de-Fonds, Switzerland
Known Models	Yema Wristmaster Slim CMM.20 (Ref: 76.24.03.SN.M, 76.24.06.SN.M, 76.24.05.SN.M, 76.24.09.SN.M), Yema Slim Diver Slim CMM.20 (Ref: 12.24.99.SN.M3), Yema Navygraf Slim CMM.20 (Ref: 22.24.66.SN.L6), Yema Superman Slim CMM.20 (Ref: 11.24.55.SN.M3, 11.24.66.SN.M3) (Add your watch to the comments below…)

The Yema caliber CMM.20 aka Calibre Manufacture Morteau 20 is 3-hander, time-only automatic movement with a micro-rotor. It is a true no-date movement.

This movement is found in various Yema watches, but was first introduced in the Superman Slim model in February 2024.

In-House?

Yema describe the cal. CMM.20 as an “in-house” movement in various pages on their site. Product pages of watches powered by this calibre mention in-house at least once or twice. For example:

“YEMA’s iconic integrated bracelet model returns in a collector’s hand-finished Limited Edition equipped with our in-house micro-rotor caliber.” –Source

And…

“The sapphire case back allows you to admire our in-house CMM.20 micro-rotor caliber while preserving a 10 BAR (100m) water resistance.” -Source same as above

Most of the other watch publications appear to follow the information given to them by the brands, so you may see this referred to as an in-house movement in various reviews.

Although exclusive to Yema, and quite close to being an in-house movement, the CCM.20 is technically is more of a manufacture caliber with some components made in-house – specifically the bridges and mainplate.

The designed and development of the movement was outsourced to independent movement engineer Oliver Mory via his own enterprise called OM Mechanics (see more below). Therefore, it is technically not considered to be a fully in-house movement.

Country of Origin:

The CCM.20 does not appear to be signed with made in France or Swiss made, although Yema describes it as a mix of French and Swiss origins – or as Yema says: “high-quality Franco-Swiss components”.

While the movement designer Oliver Mory is French, he is based in La Chaux-de-Fonds, Neuchâtel, Switzerland. Yema also states that the regulating organs are manufactured in Switzerland.

The Yema side of production is carried out in Morteau, France. This includes the making of bridges and mainplates, as well as final assembly.

In Yema’s own words:

“All CMM.20 caliber components are manufactured in France and Switzerland within a range of 72km from Morteau by recognized craftsman in fine watchmaking. The caliber bridges and mainplates are manufactured in YEMA’s workshops in Morteau where final assembly of all components takes place.” –Source

Below is an image of the CMM.20 mainplate during assembly:

It should be noted that there are some inconsistencies within Yema’s sales copy – particularly with regards to the movement design.

On their product pages, they claim:

“FRENCH MANUFACTURE – Designed, manufactured, assembled and calibrated by YEMA’s watchmakers within our Morteau workshops in France.” –Source

Then on the main CMM.20 page, they state the following:

“Entirely designed and developed by Olivier Mory in La Chaux-de-Fonds, the regulating organs are manufactured in Switzerland.” –Source

Power Reserve:

The power reserve of the CMM.20 is rated at 70 hours when fully wound. Note that this is an estimate which Yema gives a +/-10% allowance.

According to Yema, it takes about two days of consecutive wearing (8 hours per day) to fully wind the mainspring from the movement of your wrist.

This caliber can be handwound and cannot be over-wound. You can manually turn the crown clockwise about 50 times to achieve full power reserve.

Average Accuracy:

The CMM.20 is factory-regulated to have a accuracy of -3 to + seconds per day, with a maximum variation of -5 to + 10 secs/day. Yema states that any performance outside of this spec this may indicate that the watch is in need of service.

This caliber is equipped with a fairly ubiquitous ETACHRON regulator that any knowledgeable watch tech should be able to adjust if needed.

Additional Resources:

• Official CMM.20 operating instructions
• Yema CMM.20 official page