Short answer
A fake IW371485 fails on measurable details, not on looks. Measure the case, magnify the dial printing, inspect the movement through the display back, and match the caseback numbers against the paperwork. One clear mismatch is enough reason to walk away.
What the genuine watch does
The IW371485 sits in the IWC Portugieser Chronograph family, a two-register chronograph with no date window. Genuine examples carry a domed sapphire crystal with anti-reflective coating, a signed crown, and an IWC chronograph caliber visible through a sapphire caseback. Counterfeit versions copy the silhouette well and the small details poorly.
Step-by-step check
- Measure the case with digital calipers. The genuine case runs about 41 mm across and roughly 12.5 mm thick, so anything more than half a millimeter off is a warning.
- Weigh the watch head. A counterfeit case with plated alloy body or a quartz movement comes in lighter than the genuine article on the same strap.
- Magnify the dial with a 10x loupe. Check that the printed signature, the Portugieser wording, and the minute track are crisp, level, and properly spaced.
- Compare the subdial layout. The minutes counter sits at 12 and the small seconds at 6, and the hands should be thin, flat, and polished rather than stamped and rounded.
- Tilt the crystal under a lamp. Genuine sapphire shows a faint blue or purple tint from the coating and a smooth domed edge with no molding seam.
- Inspect the crown and pushers. Crown engraving should be sharp and centered, and both pushers should travel with a firm, even click.
- Open the caseback and read the movement. A genuine IWC chronograph caliber is finished and stamped with the IWC name and caliber number, while most fakes hide a generic or unmarked chronograph module or a quartz movement.
- Study the caseback engraving. Reference and serial numbers are cut deep and even on genuine watches, and the font matches IWC house style.
- Start, stop, and reset the chronograph several times. The seconds hand should snap back to zero without drift, and the minute counter should advance one step per minute.
- Check the strap or bracelet hardware. Stitching, buckle engraving, and spring bar fit are consistent on genuine pieces and sloppy on most replicas.
- Verify the numbers. Send the reference and serial to IWC or an authorized service center and ask them to confirm the combination, since IWC runs no public serial lookup.
- Sanity check the price. If the asking price is a small fraction of the current pre-owned market for the same reference, the watch is not genuine.
Red flags in online listings
- Photos that avoid the caseback, the movement, or the crown side of the case.
- Serial numbers that appear in listings from several different sellers.
- Box and papers described as lost on a watch otherwise priced as a full set.
- Dial printing that looks thick, glossy, or rotated in high-resolution photos.
- A seller who refuses third-party authentication as a condition of sale.
Before you buy
Meet at a watchmaker or an IWC service point when the deal allows it. A paid authentication costs far less than a wrong purchase, and a seller holding a genuine watch has no reason to refuse one.