Citizen Caliber 9051

Miyota/Citizen Caliber 9051

Citizen Cal 9051

Manufacturer Citizen (Miyota)
Caliber Number 9051
Similar Caliber
Miyota 9015
Movement Type Automatic
Linges
11.5”’
Diameter 26mm
Height
3.9mm thick
Jewels
24
Power Reserve
~42 hours
Vibrations Per Hour
28,800 bph (4Hz)
Lift Angle
51 degrees
Accuracy Rating
-10 to +20 sec/day
Hand-Windable? Yes
Rotor Type
Ball-bearing
Rotor Winding Direction
Clockwise (uni-directional)
Shock System Parashock
Hand Count
3
Functions Central hours; central minutes; central sweeping seconds; date calendar at 3:00
Hacking Seconds? Yes
Country of Manufacture Japan
Known Brands
Citizen Promaster (ref: NB6004-08E), Citizen Promaster Titanium Diver (ref: NB6021-17E), Citizen Promaster Mechanical Diver 1977 Challenger 200m reissue (ref: NB6021-17E, NB6021-68L), Citizen Series 8 aka 831 (ref: NB6010-81E, NB6010-81L, NB6012-18L) (Please add your watch in the comments below!)

The Citizen (Miyota) caliber 9051 is a 24 jewels 3-hand automatic movement based on the 9 series framework. This is an in-house (Citizen owns Miyota) movement, made in Japan.

Citizen Caliber 9051

Anti-Magnetic Hairspring:

Citizen states that the caliber 9051 is anti-magnetic up to 200 Gauss (16000 A/m).

In March 2021, Citizen launched a Promaster titanium diver powered by the caliber 9051. From the official announcement:

“The new Cal. 9051 movement uses anti-magnetic materials for the balance spring and surrounding components to boost the overall magnetic resistance of the watch. This new model is capable of maintaining performance even when placed 1 centimeter from a device emitting a magnetic field. The watch is also resistant to magnetic fields from everyday devices, including smartphones, and it can even be used aboard ships with magnetic compasses.” –source

On March 23, 2022, Citizen reiterated (almost word for word from the quote above) the magnetic resistant properties of the 9051 in the official press-release announcing the Promaster 1977 Challenger reissue.

Citizen Anti Magnetic Balance Spring 9051

Accuracy:

Citizen (Miyota) claims the average accuracy of the calibre 9051 to be within -10 to +20 seconds per day (not to be confused with the caliber 9050 which offers an accuracy of -5 to +10 sec/day). This information is provided with a special note stating the following:

“Accuracy measured in a stationary position. Due to the characteristics of mechanical watches, daily accuracy may be outside stated figures due to variations in conditions of use (including length of time worn, the position of the watch, wrist movement, and the winding of the spring.” –source

Replacement Prices:

As of the writing of this post, the 9051 is only available in upcoming Citizen models and is not being offered for sale by Miyota yet.

Pricing Update: Citizen released the Promaster Dive Automatic Super Titanium (NB6021-17E) on August 15, 2022 with a retail price of $795 USD. By March 2023, this model is on sale for $636 USD.

Other watches with the 9051:

On November 5, 2021, the Citizen Series 8 line was launched with the “831” series of integrated bracelet dress watches containing the caliber 9051. If there are more models not mentioned here, please add them in the comments below.

I.T Marking:

You may have noticed the “I.T” etching under the balance wheel (to the right in the image above). No, this does not stand for Information Technology. After years of wondering what it is (and nobody else on the entire Internet talking about it), Caliber Corner finally narrowed it down to: “Iida Tonooka”. This is one of two Citizen watch assembly factories: Iida Tonooka Factory and Myoko Factory. The Iida Tonooka plant is based in Iida-shi, Nagano. Myoko is in Saku-shi, Nagano.

While we’re on the topic of the prefecture  of Nagano, this would be a good time to point out that “Miyota” is the name of a town in Nagano.

Update: The I.T markings are reverting back to unsolved status. Here’s why: The I.T makes all the sense in the world to be related to the Iida Tonooka assembly plant, however, there are other stamp codes out in the wild that do not appear to correspond with any Citizen factory initials. For example, see below a gold tone 9015 with “H.E”.

Miyota Caliber 9015 Gilt Balance Wheel He

@watchaholic1991 on Instagram also sent in an image of C.U on his Miyota caliber 9075.

Miyota 9075 C U Date Code Watchaholic1991

For this reason, I.T and all other markings are still unsolved and Caliber Corner will be reaching out to Citizen Watch Co. for any information they are willing to provide.

Typically, letter codes like this end up being manufacturing date codes, but it does not make sense with the 3 known codes here. Iida Tonooka Factory does make sense, but only for the I.T stamps. As soon as more information is discovered, it will be posted here! If it is significant, an entire post will be created on the topic. Thanks to all who have helped!

Date Code Theory:

If it is in fact a date code, it could be X.Y = month.year

So Far we have the samples: I.T / H.E / C.U.

I/H/C can be months since they are all letters within the first 12 letters of the alphabet.

A1 B2 C3 D4 E5 F6 G7 H8 I9 J10 K11 L12

So, anything after that will eliminate the date code theory: MNOPQRSTUVWXYZ (letters that can’t be months).

The year gets tricky:

The I.T stamped movement featured in this caliber listing was found in a model that was released 0n 8/15/2022. The watch includes paperwork indicating that it was originally sold in 12/2022. So, with the date code theory, that would place the “T” at 2022 (maybe 2021, but doubtful).

A2003 B2004 C2005 D2006 E2007 F2008 G2009 H2010 I2011 J2012 K2013 L2014 M2015 N2016 O2017 P2018 Q2019 R2020 S2021 T2022 U2023 V2024 W2025 X2026 Y2027 Z2028

Interestingly, this Miyota 90S5 found in a Kurono watch has no markings. Not sure how that plays into the date code theory.

However:

In Japan, the date is written with the year first. Therefore, if the date theory is correct, it could be X.Y = year.month

But this doesn’t add up since the second letters T and U from the samples above are after the month cutoff.

Additional Resources:


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List of Miyota Movements Watch Movement | Caliber Corner
7 months ago

[…] 9051 – Anti-magnetic hairspring […]

Magnus
Magnus
7 months ago

16000 gauss? Do you not mean 16000 a/m?

Matt Farmer
Matt Farmer
6 days ago

I don’t have a watch with the same 9051 but I found you on Instagram and I am loving following your research on the two letter code on the movement. I agree that it seems factory related but I am here for the sleuthing in real time! Keep up the great work, love the site!

;
Venus Caliber 178

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