Quick answer
The number 8240029 is not a standard Cartier model reference. Cartier references for the Tank line follow an alphanumeric pattern such as W5200029 or WSTA0042, where a letter prefix points to the collection and the case material. A bare seven digit string in a listing title is usually a seller code, a marketplace SKU, or a case serial stamped on the back of an older watch. That alone does not make the watch fake, but it does mean the listing gives you nothing verifiable. Ask the seller for the reference stamped on the caseback and the serial beside it before you go any further.
If the price sits far below the going rate for that Tank model, treat a replica as the likely outcome. Most fakes fail in three places, in this order: the caseback engraving, the crown cabochon, and the movement.
What you need before you start
- A 10x jeweler's loupe or a phone camera with a macro lens
- Bright, indirect light and a plain background
- Clear photos of the dial, caseback, crown, clasp, and both case flanks
- The seller's stated reference number and serial number, in writing
How to check a Cartier Tank in seven steps
- Request a straight-on photo of the caseback and read the reference and serial yourself instead of trusting the listing text.
- Match that reference against Cartier's own Tank model list and confirm the case size and metal line up with it.
- Study the caseback engraving through the loupe and confirm the letters are crisp, evenly spaced, and cut into the metal rather than printed on the surface.
- Inspect the dial and check that the Cartier signature, the Swiss Made text, and the Roman numerals are sharp with no fuzzy edges or uneven gaps.
- Examine the crown and confirm the blue cabochon is a polished synthetic spinel set flush into the metal, not a plastic dome glued on top.
- Open the caseback or ask for a movement photo, then confirm the movement maker and finish match what that reference should carry.
- Hold the watch and check the bracelet or strap hardware for solid construction, correct hallmarks, and a clasp that opens and closes cleanly.
Red flags that decide it
- Engraving that looks laser printed, shallow, or slightly crooked
- A cabochon that is oversized, flat, or the wrong shade of blue
- Roman numerals with wrong proportions, most often the VII and the IX
- A quartz movement inside a reference that should be mechanical
- Papers or a box with wrong font weight, wrong logo spacing, or a serial that does not match the case
- A seller who dodges direct questions about the reference and serial
Getting a professional verdict
Cartier boutiques and authorized service centers can verify a reference and serial, and they can service the watch if it is genuine. Independent watchmakers who handle Swiss brands can also open the case and confirm the movement. On higher value Tanks, a written appraisal from a specialist dealer or an auction house watch department adds a second opinion. Arrange that inspection before you send any money.
One last point on price. A genuine steel Cartier Tank in good condition trades inside a defined range that you can check against completed sales on dealer sites and auction results. A listing at a small fraction of that range is the strongest single signal you will get, and it usually arrives before you ever see the watch in person.