An Omega reference is fourteen digits in six groups, and each group encodes one attribute: collection, case and bracelet material, diameter, movement, dial colour, and a sequence number. Omega publishes the codification itself. Once you can read it, a string such as 231.10.39.21.03.001 stops being a serial number and becomes a specification.
This matters more for the Aqua Terra than for almost any other Omega, because two of the groups behave in ways that catch buyers out. A "39" Aqua Terra is not a 39 mm watch. And several references commonly searched alongside the Aqua Terra are not Aqua Terras at all.
The structure
The format is AAA.BB.CC.DD.EE.FFF. Omega calls it the Long Product Identification Code, or PIC. Note that it is fourteen digits, not fifteen: 3 plus 2 plus 2 plus 2 plus 2 plus 3.
| Group | Digits | Meaning |
|---|---|---|
| A | 3 | Watch line or family |
| B | 2 | Material of the watch head and of the bracelet or strap |
| C | 2 | Diameter, rounded |
| D | 2 | Movement type and calibre |
| E | 2 | Dial colour and material |
| F | 3 | Sequence number |
Group A: the collection
| Code | Collection |
|---|---|
| 210 | Seamaster Diver 300M |
| 215 | Seamaster Planet Ocean 600M, Master Chronometer generation |
| 220 | Seamaster Aqua Terra 150M, Master Chronometer generation |
| 231 | Seamaster Aqua Terra 150M, Co-Axial 8500 generation |
| 232 | Seamaster Planet Ocean 600M, Co-Axial 85xx generation |
| 310 | Speedmaster |
This is the single most useful group. If a listing describes 232.30.42.21.01.001 as an Aqua Terra, the listing is wrong. That reference is a Planet Ocean 600M.
Group B: case and bracelet material
The logic is first digit for the case material, second digit for what it is attached to.
| Code | Meaning |
|---|---|
| 10 | Stainless steel, assorted metal |
| 11 | Stainless steel, other metal |
| 12 | Stainless steel, non-metal, no CITES |
| 13 | Stainless steel, non-metal, CITES |
| 20 to 23 | Stainless steel and gold, following the same pattern |
| 30 to 33 | Stainless steel and another material |
| 50 to 53 | Gold |
| 90 to 93 | Other material |
The CITES distinction is the detail nobody explains, and it is quietly the most useful. Non-metal without CITES means rubber, fabric or calf. Non-metal with CITES means a strap using a species regulated under the Convention on International Trade in Endangered Species, which in practice means alligator. You can therefore read the strap material off the reference before you see a photograph. 231.13.39.21.01.001 is on alligator. 220.12.43.22.03.001 is on rubber. Both check out.
Group C: diameter, and the trap
Omega rounds the case diameter to two digits by ordinary mathematical rounding. That produces the following, which is where Aqua Terra buyers get caught:
| Code | Actual diameter |
|---|---|
| 38 | 37.5 mm |
| 39 | 38.5 mm |
| 40 | 39.5 mm |
| 41 | 41 mm |
| 42 | 41.5 mm |
| 43 | 43 mm |
There is no 39 mm or 40 mm Aqua Terra. If a listing advertises a "39 mm Aqua Terra" with a 231.10.39 reference, the seller has read Group C literally on a 38.5 mm watch. The same applies to "42 mm" on a 231.10.42 reference, which is 41.5 mm. This is not a fake, it is a description error, but it tells you something about how carefully the listing was prepared.
Group D: movement
The first digit indicates movement type, the second the calibre or complication. Across the Aqua Terra range in practice, 21 appears with calibres 8500 and 8900, 20 appears with 8520 and 8800, and 22 appears with the 8938 Worldtimer.
One popular reading of Group D holds that the second digit counts complications. That does not survive contact with this collection: both 20 and 21 references carry a date. We treat Group D as tracking the calibre family, and say so as an observation rather than as a published Omega rule.
Group E: dial colour
| Code | Colour | Code | Colour |
|---|---|---|---|
| 01 | Black | 07 | Coloured mother-of-pearl |
| 02 | Silver | 08 | Champagne |
| 03 | Blue | 09 | Ivory |
| 04 | White | 10 | Other colours |
| 05 | White mother-of-pearl | 11 | Red |
| 06 | Grey | 13 | Brown |
Codes 51 to 63 repeat the same range with precious stones. Green dials use 10, "other colours", which is why the green 41 mm reads 220.10.41.21.10.001.
What the reference does not tell you
The PIC does not encode the calibre reference itself, the production year, the water resistance, or which non-metal a strap is made of. For those you need the papers, the caseback, or the watch in hand.
What "teak" actually means
Omega's own wording, from the current product pages: the dial "is distinguished by a horizontal 'teak' pattern which is inspired by the wooden decks of luxury sailboats". On the older 231 series pages Omega uses a formal proper noun, the Teak Concept pattern. That nomenclature shift is a small but reliable tell of which generation you are reading about.
Three points that copy across the market frequently gets wrong:
- The stripes changed direction in 2017. The 8500 generation runs vertical and deeply engraved. The 2017 Master Chronometer redesign rotated them to horizontal and made them shallower.
- The Worldtimer kept vertical stripes, even though it belongs to the current 220 generation.
- The teak dial is not universal to the Aqua Terra. Since 2022 Omega has shipped the Shades colourways, the 2024 black lacquer dials and the 2025 ceramic-bezel turquoise with no teak pattern at all. Copy describing "the Aqua Terra's signature teak dial" needs to be scoped to the models that actually have one.
The two generations, side by side
| 231 series, Co-Axial 8500 | 220 series, Master Chronometer | |
|---|---|---|
| Introduced | Late 2000s | Announced Baselworld 2017, detailed August 2017 |
| Case sizes | 38.5 mm, 41.5 mm, 43 mm GMT | 38 mm, 41 mm, 43 mm Worldtimer, plus 28, 30 and 34 mm |
| Calibre | 8500, 60 hours. Later Master Co-Axial versions resist 15,000 gauss. | 8900 in 41 mm, 60 hours. 8800 in 38 mm, 55 hours. |
| Date position | 3 o'clock | 6 o'clock |
| Teak stripes | Vertical, deeply engraved | Horizontal, shallower |
| Case | Asymmetrical, crown partly absorbed into the caseband | Symmetrical, lyre lugs, conical crown |
| Certification | Chronometer, later Master Co-Axial | METAS Master Chronometer, 0 to plus 5 seconds per day |
| Water resistance | 150 m, screw-in crown | 150 m, screw-in crown |
The anti-magnetic story is worth getting right, because two milestones are routinely conflated. In 2013 Omega released the Aqua Terra greater than 15,000 Gauss, calibre 8508, a single dedicated model. Then on 31 March 2014 the Master Co-Axial calibres rolled out across eight movements using Nivagauss components, bringing 15,000 gauss resistance to the Aqua Terra as a range. That is why the 231 series splits into pre-Master and Master Co-Axial variants distinguished only by the final three digits.
Reference by reference
Verified against Omega's own product pages, 26 July 2026.
| Reference | Collection | Size | Dial | Fitted to | Calibre |
|---|---|---|---|---|---|
| 231.10.39.21.02.001 | Aqua Terra 150M | 38.5 mm | Silver teak | Steel bracelet | 8500 |
| 231.10.39.21.03.001 | Aqua Terra 150M | 38.5 mm | Blue teak | Steel bracelet | 8500 |
| 231.10.39.21.03.002 | Aqua Terra 150M | 38.5 mm | Blue teak, sun-brushed | Steel bracelet | 8500 Master Co-Axial |
| 231.13.39.21.01.001 | Aqua Terra 150M | 38.5 mm | Black teak | Black alligator | 8500 |
| 231.13.39.21.02.003 | Aqua Terra 150M | 38.5 mm | Silver teak | Brown alligator | 8500 Master Co-Axial |
| 231.10.42.21.03.001 | Aqua Terra 150M | 41.5 mm | Blue teak | Steel bracelet | 8500 |
| 231.10.42.21.03.003 | Aqua Terra 150M | 41.5 mm | Blue teak, sun-brushed | Steel bracelet | 8500 Master Co-Axial |
| 231.10.42.21.01.003 | Aqua Terra 150M | 41.5 mm | Black teak, sun-brushed | Steel bracelet | 8500 Master Co-Axial |
| 220.10.43.22.03.001 | Aqua Terra Worldtimer | 43 mm | Blue, vertical teak | Steel bracelet | 8938 |
| 220.12.43.22.03.001 | Aqua Terra Worldtimer | 43 mm | Blue, vertical teak | Blue rubber | 8938 |
All eight 231 references above are time and date only. None is a GMT or a chronograph. All carry a screw-in crown, 150 metres, and a display caseback.
Four references frequently searched as Aqua Terras that are not
| Reference | What it actually is |
|---|---|
| 232.30.42.21.01.001 | Planet Ocean 600M, 42 mm, ceramic diving bezel, calibre 8500, helium escape valve |
| 232.30.38.20.01.001 | Planet Ocean 600M, 37.5 mm, calibre 8520 |
| 215.30.40.20.04.001 | Planet Ocean 600M, 39.5 mm, white ceramic dial and bezel, calibre 8800 |
| 210.22.42.20.01.001 | Seamaster Diver 300M, 42 mm, steel and 18K yellow gold, Ceragold bezel, calibre 8800 |
Note the Group B code on that last one. The 22 tells you it is steel and gold before you read a word of the description.
A related point on naming: "Skyfall" and "Spectre" attach to several of these references in collector shorthand and in Omega's own page metadata. Outside of the genuinely numbered limited editions, they are film associations rather than official model designations. Read them as shorthand, not as provenance.
What this is worth at market
Current authorised retail for a steel Aqua Terra 150M on bracelet is 7,100 US dollars in both 38 mm and 41 mm, observed on omegawatches.com and at an authorised retailer on 26 July 2026. Lacquered and turquoise dials sit at 7,400 dollars, and the 38 mm Summer Blue at 7,800 dollars. Note the counter-intuitive result: the most expensive steel-bracelet Aqua Terra is a 38 mm.
Pre-owned, from a sweep of US dealer asking prices on 26 July 2026:
- 231 series, 41.5 mm steel on bracelet: roughly 3,800 to 5,000 US dollars
- 220 series, 41 mm steel on bracelet: roughly 4,725 to 6,650 US dollars
- 220 series, 38 mm steel on bracelet: roughly 5,160 to 6,495 US dollars
Against a 7,100 dollar list, a recent lightly worn current-generation example sits around 85 to 91 per cent of retail, and an older 2021-era example closer to 62 to 67 per cent. Bob's Watches publishes an aggregate average Aqua Terra sale price of 4,564 US dollars with 74 per cent of sales falling between 2,000 and 5,000 dollars, which reflects how much of the installed base is 231 series.
One caution: several dealer sites still quote Aqua Terra retail as 6,700 or 6,800 US dollars. Those figures are stale. Calculate any discount from Omega's own current figure.
Frequently asked questions
How many digits is an Omega reference number?
Fourteen, in six groups: three, two, two, two, two, three.
What size is a 231.10.39 Aqua Terra?
38.5 mm. Group C is a rounded figure, not the actual diameter.
What is the difference between 231 and 220 Aqua Terra references?
231 is the Co-Axial 8500 generation with vertical teak stripes and the date at 3 o'clock. 220 is the 2017 Master Chronometer generation with horizontal stripes, the date at 6 o'clock, a symmetrical case and METAS certification.
Is the Aqua Terra a dive watch?
No. It is rated to 150 metres with a screw-in crown, which covers swimming and surface water sport comfortably, but it has no rotating timing bezel and carries no ISO 6425 certification. Read our guide to water resistance ratings.
What does 231.13 mean?
Stainless steel case on a CITES-regulated strap, which in practice means alligator.
Which Aqua Terra generation should I buy pre-owned?
The 231 series buys more watch per dollar and has the deeper, more three-dimensional teak dial. The 220 series brings METAS certification, the symmetrical case and the date at 6 o'clock. Neither is the correct answer for everyone. Condition, completeness and service history matter more than the generation.
Currently at Honeyrock
- Aqua Terra 38.5 mm, blue teak, Ref. 231.10.39.21.03.001, full set
- Aqua Terra 38.5 mm, black teak on alligator, Ref. 231.13.39.21.01.001
- Aqua Terra 41.5 mm, blue teak, Ref. 231.10.42.21.03.003
- Aqua Terra 41.5 mm, black teak, Ref. 231.10.42.21.01.003
- Aqua Terra 38 mm, blue dial, Ref. 220.10.38.20.03.001
- Aqua Terra Worldtimer 43 mm, Ref. 220.10.43.22.03.001
- Planet Ocean 600M 42 mm, Ref. 232.30.42.21.01.001
- All Omega at Honeyrock
Sources
- Omega, "Find information about the brand and your product", customer service FAQ, codification tables.
- Omega, individual product and archive pages for each reference cited, observed 26 July 2026.
- SJX, "Omega introduces facelifted Aqua Terra", 23 August 2017.
- Monochrome, Aqua Terra 150M reviews 2017 and 2018, and "Omega goes anti-magnetic with the Master Co-Axial calibres", 31 March 2014.
- Quill and Pad, "Decoding Omega references: 14 magic digits".
- Bob's Watches, Aqua Terra market page, observed 26 July 2026.
- Watchfinder and Co, The 1916 Company and European Watch Company listings, observed 26 July 2026.
Retail figures are authorised retail observed on the date given. Pre-owned figures are dealer asking prices, not transacted values, and are provided as market context only. Honeyrock Luxury makes no claims about future value or price appreciation. Last updated 26 July 2026.
