Short answer
A fake IW371772 is a counterfeit copy of the IWC Portugieser chronograph reference IW371772. A genuine watch carries that reference and a matching serial engraved into the caseback, runs an IWC chronograph caliber, and is built to tolerances a replica shop does not reach. Copies match the dial layout and the case silhouette from a few feet away. They fail on engraving depth, movement finishing, part fit, weight, and paperwork. If you own the watch and want a verdict, take it to an IWC authorized dealer or an independent watchmaker with an IWC parts account.
Prerequisites
- A 10x jeweler's loupe
- Digital calipers and a gram scale
- Clear photos of a verified genuine IW371772 at the same dial variant
- A soft cloth and a lint-free surface
Checks, in order
- Weigh the watch on a gram scale with the strap removed. Counterfeit cases often use a lower-density alloy, so the head reads light for its size.
- Measure case diameter, thickness, and lug width with calipers. Compare each figure to the published specification for the reference.
- Examine the caseback engraving under the loupe. Genuine reference and serial numbers have crisp edges, even depth, and consistent spacing between characters.
- Inspect the dial printing. Look for sharp serifs on the brand name, even paint fill in the minute track, and a clean step between the dial and the flange.
- Check the applied indices and hands. Each marker should sit flush, reflect the same tone, and align with the minute track. The chronograph hands should rest at zero when the pusher is used to reset.
- Wind the crown and operate both pushers. Threads should engage without grit, and the pushers should return with a short, firm stroke.
- Look through the display back at the movement. Check rotor engraving, perlage or Geneva striping on the bridges, and the shape of the balance and escapement area.
- Tilt the crystal under a lamp. Anti-reflective coating on a genuine sapphire crystal produces a faint blue or purple cast and does not show rainbow swirls.
- Examine the strap, buckle, and spring bars. Stitching should be even, the buckle tang should be signed, and the spring bars should seat without play.
- Cross-check the caseback number against the warranty card and any service record. Numbers that do not match, or that return no record at IWC, end the inspection.
- Hand the watch to an authorized dealer or watchmaker and ask for a written opinion on authenticity.
Where replicas fall short
Counterfeit Portugieser chronographs tend to get the overall proportions close and the details wrong. Common tells include shallow laser engraving on the caseback, printed rather than applied indices, subdials that sit too far apart, and a rotor with soft lettering. Movement finishing is the hardest part to copy, so a close look through the caseback settles most questions.
Legal and resale notes
Buying or selling a counterfeit watch is a trademark violation in the United States, and shipments can be seized by customs. A counterfeit carries no factory service, no parts support, and no resale value beyond the price paid. When the price on an IW371772 sits far below the market for the reference, treat that as evidence rather than a bargain.