How to Identify a Vintage Omega 
Omega is a great brand. Both the new and the vintage models are fantastic.
However, if you buy a new one from an AD or boutique, the risk of buying a lemon is very low. You can buy one with a factory flaw, but that’s out of your hands. With vintage Omegas, it’s anything but easy. Nevertheless, I’d like to provide some guidelines.
In this article, I’ll show you exactly how to identify a vintage Omega watch.
This article was originally published on April 20, 2019. It was updated and newly published on November 14, 2019.
- Identifying the movement
- Serial numbers
- 30mm movements
- 60X series
- Rotor automatics and their issues
- Location of the markings
- Case serial numbers
- Case material codes
- 3-, 4-, and 5-digit reference numbers
- The 6-digit system
- American market references
- Two references on one case?
- A collection-specific number on an unsigned watch
- Locally made cases
- The calibre doesn’t match the case
Identifying the movement
Please don’t buy a vintage watch, let alone an Omega, without having a look at the movement. If you ask the seller for pictures of the movement, and you get a response like “I can’t” or “I don’t have the tools” or just a plain “no,” it’s best to skip that one.
Omega movements, from the 1930s and 1940s, usually have the calibre number under the balance. From the late 1940s on, the number was located on one of the bridges, often the same one as the serial number.
Every Omega movement has a serial number. In pocket watches from the early 1900s, you can find it on the dial side of the baseplate. In other words, you have to disassemble the watch to access it. Later on, the serial was always on one of the bridges.
You can find a list of serial numbers for Omega at Chronomaddox, a useful Omega resource created by the late Chuck Maddox. Note that this list doesn’t apply to Speedmasters.
Speedies have a separate list, compiled by Roman Hartmann, and you can check it here.
The 30T2 and its derivatives are a legend in their own right. They can be tricky, though.
30T2 and derivatives
Note that various versions of the calibre 30T2 sometimes have a signature of the base calibre, while that’s not necessarily the full calibre number. For example, the 30T2 PC and 30T2 PC AM are both signed 30T2 PC, because the only difference is an anti-magnetic balance in the AM version.
The Ranfft movement archive entries for movements of various Omega families list differences between particular movements of a calibre family. It’s always good to check that out when looking at a movement.
For example, when you see a cal. 265 with a flat hairspring, while it’s supposed to have a Breguet overcoil, you can be sure that it’s a 269 movement with the wrong balance.
The 30T2 had a few chronometer versions, all of a higher grade than the non-chronometer versions. These have the suffix RG in the number. You can easily recognize the RG by its distinctive regulator.
I’ve encountered cases where a dial signed “Chronometre Omega” was fitted to a non-RG 30mm movement. This is – and will always be – wrong. A non-RG 30mm movement + a “chronometre” dial = frankenwatch. No exceptions.
This is nothing more than a 5XX base without the automatic winding assembly. Of course, the barrel is different as well. They were mostly used in the Geneve collection. However, a few Seamaster De Ville models had it as well.
Theoretically, it fits in a case intended for a 5XX. If you see a 60X series movement in a case with a reference that tells you it’s a model which is supposed to be equipped with a 5XX-series automatic, that’s wrong.
Until the 1990s, the only supplier of chronograph movements for Omega was Lemania. One of the best-known ones is the cal. CH27 C12, later known as the cal. 321. There are, however, differences between the CH27 C12 and the 321.
The 321 is always marked as such and always has copper-colored plating. So, if you’re checking out an Omega chronograph from the 1950s, which is supposed to have a cal. 321, but it has a silver-colored finish on the plates, cocks, and bridges, and it doesn’t have the 321 markings, it’s simply not a 321.
Rotor automatics and their issues
Omega’s rotor automatics of the 5XX family (and everything that followed) are great. Still, they have a few problems worth noting.
You need to be extremely careful with signs of issues with the rotor. The one thing that’s known to go wrong with these movements is the axle of the rotor. When it wears out, the rotor will start rubbing against the bridge on which it sits (upper bridge for automatic device), and against the case back. The edge on the rotor will have a noticeable loss of plating. So will the upper bridge, most likely. The inner side of the case back will have a characteristic circular trace on it.
When you see that, best skip that one. It may be that the issue has been repaired. But can you be sure? Nope.
It’s also not uncommon to see movements built from spare parts. You can often spot them by an inconsistent tone of the plating throughout the various components. Of course, some parts will change color due to the different solutions they were cleaned in during a service. However, if one part has an almost yellow gold color, and the other one has a deep, dark copper tone, you can be sure they didn’t leave the factory together.
Another example of frankenising is using parts from Tissot counterparts in movements, which the two brands shared. Notably, that’s the case with the Omega 1480 and the Tissot 2471. Well, technically they’re the same thing. So, the parts are interchangeable.
I’ve seen rotors from the Tissot transplanted in an Omega. If you see something like that, skip that one.
Location of the markings
The general rule is that Omegas have all the relevant markings on the inner side of the case back. These should include a reference or serial number, the Omega stamp in a triangular frame, and the case material. Sometimes, and that usually applies to the 1950s and 1960s pieces, you can also find some info about the manufacturer of the case.
Some pieces don’t follow this pattern. For example, the two collections made for the Swedish market – the Suveran, and the Officer. These had the markings on the outside of the case back.
Also, many US market models were cased locally, in cases made by American suppliers. These often had the case material marked on the outside.
Case serial numbers
While Omega’s reference numbers start somewhere in the 1930s, they were usually not placed on the watch itself until the mid-1940s. Notable exceptions include the Naiad and Medicus models, which did sometimes have the reference stamped on the case back.
The case serials follow the same code as the serial numbers found on movements. There shouldn’t be much of a gap between the case and movement serial – 2 years tops. Note that if it’s three, for example, that doesn’t disqualify the watch. Omega has a record of pairing movements and cases from batches made within a considerable period.
While the reference numbers started to appear on cases regularly in the mid-1940s, the latest serial-stamped cases I’ve seen dated to 1947-1948. This especially applies to chronometers equipped with the 30T2 RG (all variants of the RG).
Case material codes
A two-letter case material code preceded every Omega reference. This was rarely found on the case.
It was also – at times – not very consistent. For example, with 3-, 4- and 5-digit reference numbers, the standard code for stainless steel was CK. Still, there were models in stainless steel, where the code was MI.
For watches made until the early 1960s, the codes were as follows:
- Steel: CK/MI
- Solid gold: OT/OJ
- Gold cap: KO
- Gold-filled: PK
Remember that if a reference was made in a few case material versions, the base reference number will always be the same.
So, let’s assume that you’re checking a 4-digit reference in the Omega Vintage Database (OVD) on the Omega website. The only result is a watch in solid gold, while the one you’re looking at is stainless steel. This doesn’t mean that there’s anything wrong with the watch. It’s just that you’re looking at a CK, the steel version, and the watch that is listed in the OVD is an OT/OJ, in other words, a version in solid gold.
The OVD misses plenty of entries, both entire models and different versions of listed watches.
3-, 4-, and 5-digit reference numbers
It’s unknown if these reference numbers have any meaning. I don’t suppose they’re completely random, but there aren’t any means of decoding them.
The four-digit references were used until the early 1960s.
In the late 1950s, Omega introduced a short-lived 5-digit system, paired with the same material codes as the 4-digit system. It was mostly phased out by 1962/1963.
The 6-digit system
In 1962, Omega introduced a new system of case reference numbers. By the 1970s, it was changed again, to a 7-digit system.
Still, the principle remains the same for both systems, that the first three digits define the characteristics of a watch. A key for this can be found here, along with case material codes for 6- and 7-digit reference numbers.
So, if you look at the ordinary Speedmaster reference, 145.022, 145 means: (1)Gent’s watch (4) Manual winding chronograph (5) Water-resistant.
Keep in mind, that the OVD might require you to add a 0 after the period in a 6-digit reference to look it up. For example, a 145.022 becomes 145.0022 in the search.
American market references
While models with ordinary reference numbers were available in the US, Omega has made some watches for the US market only. Only a few of these are listed in the OVD.
Usually, the references of these models had the prefix “G.” If you come across one of these, chances of finding it in the OVD are slim. Again, this means that a watch isn’t listed there, which sadly isn’t uncommon.
Two references on one case?
That’s not unheard of. Some cases were used for two different models. The difference between them could be a completely different dial and handset. Sometimes, though, it was the movement.
Now and then, one reference could have been used with two or three different movements. Apart from one reference spanning over two or three generations of a used movement, this is also the case with pieces made for the US market. The movement in these had a different number due to a different (lower) jewel count. They had fewer jewels to avoid a higher import tariff in the US.
A collection-specific number on an unsigned watch
What if the watch you’re looking at has a reference number that tells you it’s a Seamaster, but it doesn’t say Seamaster on the dial? That’s quite common. One reference could have belonged to two collections at the same time (for example, Seamaster and Geneve), and yet the watch was also available with no collection name on the dial.
A noteworthy example of a shared reference is the Seamaster 600, which was also available as a Geneve. But there, the Seamaster always had the hippocampus logo on the back. A plain back + Seamaster 600 dial = a “franken” or a redial.
Keep in mind that a reference that was shared between different collections was a thing of the 1960s and 1970s. In the 1950s, a Seamaster reference on a watch with an unmarked dial only means that the watch was available without the collection name. Also, for a Seamaster made before ca.1958, the absence of the hippocampus logo is OK. That logo appeared on SM cases only from very late in 1957.
It’s the year of introduction that matters. For a reference introduced before 1957, the absence of the logo on a specimen from 1958 or 1959 is nothing strange.
Locally made cases
This only applies to watches that were made for the US and UK markets. Steel cases were always made in Switzerland, along with the rest of the watch. However, gold-plated and gold-filled ones for the US market were made by local suppliers, like Wadsworth.
In the UK, solid gold cases, especially the ones with the typical British purity of 9ct, were made locally by Dennison (ALD). A Dennison Omega case always has the following markings:
- Omega stamp
- Reference or serial number
- Purity mark
- Assay office stamp (London, Birmingham, Glasgow, etc.)
- A “date letter” corresponding to the year of manufacture of the case. Every assay office had a different letter assigned to a specific year.
The calibre doesn’t match the case
The first and most obvious reason for that is that the watch is a “franken,” which means that it has been assembled from random parts
However, there’s one exception.
Always check if the movement in the watch isn’t a US version of the movement mentioned in the OVD. These will have a US import code (OXG) on the balance cock, and a lower jewel count. The OVD often doesn’t list the US version of a particular reference.
This is true for almost all families of Omega rotor automatics: 4XX, 50X, 55X, 56X, 59X, 71X, and 1XXX series. For example, the jewel count is the only difference between the 470 and 471, 490 and 491, 550, and 552. And so on.
You can find the details of the differences in the Ranfft archive. Every entry for movements within a particular family list the differences between the movements within that family.
Otherwise, as mentioned in the previous part of the series, a movement that doesn’t match the case is a red flag.
Keep in mind that some vintage models are faked very often, especially the Constellation. These fakes will often check all the boxes for the marking patterns described above, but some details will tell you it’s a fake.
You can find a detailed guide to authenticate Constellation cases at Omega Constellation Collectors, which is the resource for Constellations.
All of this might seem very complicated. Still, authenticate/identify some watches for the sport of it. As a challenge. After some time, it’ll sink in and become second nature.