A fake IW371643 is a counterfeit copy of the IWC Portugieser Chronograph, a 41 mm stainless steel watch with a vertical bicompax layout and an in-house automatic movement. The genuine watch runs IWC calibre 69355 with a 46-hour power reserve, sapphire crystal on both sides, and a 30 m water-resistance rating. Counterfeits typically fail on three points: the movement, the caseback engraving, and the precise spacing of the subdials at 12 and 6 o'clock.
Is IW371643 a Real IWC Reference Number?
IW371643 belongs to the Portugieser Chronograph 3716 family, the line that moved to the in-house 69355 calibre in 2020. Reference numbers in this family change with dial color, case metal, and strap, so two watches that look alike can carry very different numbers.
The safest check is to match the full reference against IWC's own product data rather than a photograph. A seller who cannot show the exact IW371643 number on the caseback and the guarantee card is already a red flag.
How Do You Spot a Fake IWC Portugieser Chronograph?
Case and caseback
Genuine cases are machined from stainless steel or gold with crisp, even lug bevels and a polished bezel that sits flush with the crystal. Engraving on the caseback is cut to a consistent depth, with the reference and serial numbers evenly spaced.
Counterfeit cases often show soft or rounded lug edges, a bezel that sits slightly proud, and shallow, overly wide engraving. The display back on a fake may also be mineral glass, which scratches easily and lacks the anti-reflective coating used on the genuine sapphire.
Dial, hands, and subdials
The genuine dial uses applied polished indices, sharp printed text, and a clean sunray or lacquer finish depending on the variant. The subdials sit at 12 for chronograph minutes and 6 for small running seconds, with fine concentric snailing inside each.
On fakes, subdial centers are often off-axis, snailing is coarse or absent, and the "IWC" and "SCHAFFHAUSEN" printing looks heavy or blurry under a loupe. Leaf-shaped hands should be mirror-polished with clean edges and no burrs at the tips.
Movement
A real IW371643 shows calibre 69355 through the caseback: a 4 Hz automatic with 46 hours of reserve, Cotes de Geneve striping on the bridges, and an engraved rotor. Counterfeit Portugieser chronographs almost always hide a Valjoux 7750 derivative behind a solid or poorly finished back.
A 7750-based copy carries a distinctive rotor wobble and a stiff pusher feel. The genuine 69355 starts smoothly, hacks when the crown is pulled, and resets to zero instantly.
Why Do Most Fakes Get the Movement Wrong?
Producing an integrated in-house automatic chronograph at counterfeit price points is not economically viable, so copies substitute a mass-produced 7750 clone. That substitution usually makes the case noticeably thicker than the genuine profile, which shows up on the wrist and in side-profile photos.
How Should You Verify an IW371643 Before Buying?
- Request a clear macro photo of the caseback showing the reference and serial numbers, plus a movement shot.
- Match the full reference to IWC's official product page and confirm the dial and metal combination.
- Check that the serial number matches on the watch and the IWC guarantee card.
- Have the watch inspected by an IWC boutique or authorized service partner, then register it under My IWC for the extended warranty.
- Buy from an authorized dealer or a pre-owned seller with a documented return and authentication policy.
Authentication specialists examine movement finishing, case geometry, and service history together, which is far more reliable than any single visual tell.