Search "fake iw371736" and you get pages of listings and almost no explanation. The short answer: IW371736 is not a reference IWC publishes. It reads like a mashup of the Portugieser Chronograph family codes, mostly IW3714xx from the Valjoux years and IW3716xx from the current generation. A "fake IW371736" is, in practice, a counterfeit Portugieser Chronograph: 41 mm steel case, two subdials, no date.
The genuine watch behind the number
The modern Portugieser Chronograph is a 41 mm stainless steel watch, roughly 13 mm thick, water resistant to 30 m, with sapphire on both sides. The dial carries two registers, chronograph minutes at 12 and running seconds at 6. There is no date window, no third subdial, and no day indicator. Hands are leaf shaped, and the numerals at 12 and 6 are applied rather than printed. Inside sits calibre 69355, a column wheel chronograph with a 46 hour power reserve. The older IW3714 references used calibre 79350, which was built on a Valjoux 7750 base.
Where the numbering falls apart
IWC reference numbers run as IW plus six digits. The first four digits identify the family; the last two identify dial and case variation. That is why you see IW371605, IW371617, IW371620 and similar, but not IW371736. Sellers who write it that way are usually copying a listing, transposing digits, or inventing a code that sounds specific enough to rank in search.
The tells that matter most
- Subdial count and position. A stock 7750 places a running seconds hand at 9. On a real Portugieser Chronograph that subdial does not exist. Three registers means fake.
- Date window. Any date at 3 on a watch claiming this reference is wrong.
- Case thickness. Valjoux based fakes often run 14 to 15 mm because the movement and its rotor stack need the room.
- Dial printing. Compare the weight of the IWC wordmark, the spacing of "SCHAFFHAUSEN," and the crispsness of the minute track under magnification. Fakes tend to look heavy or soft.
- Crystal. Genuine sapphire has anti reflective coating on both faces and stays clear at an angle. Cheap fakes look milky or carry a strong blue tint.
- Caseback engraving. Depth and sharpness vary, and the reference digits stamped inside rarely match the listing.
- Crown feel. Winding and setting should be smooth and precise, with a signed crown and a clean click at each position.
What "Swiss movement" usually means
In the counterfeit trade the phrase covers several different things: an Asian 7750 with a decorated rotor, a stripped movement dropped into a new case, or a genuine ETA 7750 pulled from a donor watch. None of them are calibre 69355. Parts support does not exist for these builds, so service is a matter of finding someone willing to work on an unknown assembly. Water resistance is a claim, not a measurement.
Practical and legal reality
In the United States, trafficking in counterfeit goods is a federal offense under 18 U.S.C. 2320, and shipments are routinely seized by Customs and Border Protection. Reselling a counterfeit as genuine adds fraud exposure on top of that. If you are trying to verify a watch you already own, the useful step is a movement inspection by a watchmaker who handles IWC, plus a check of the reference stamping against the dial configuration. If the subdials, the date, or the thickness do not line up, the number on the listing will not save it.