Short answer
A fake IW371628 fails on measurements and finishing, not on the logo. Run four checks before you pay: measure the case, read the caseback engraving, compare the subdial centers, and test the chronograph reset. Counterfeits of the IWC Portugieser Chronograph almost always miss at least one of these.
What the reference should be
IW371628 sits in the IWC Portugieser Chronograph family. Expect a stainless steel case of 41.0 mm, a vertical two-register dial with running seconds at 6 and chronograph minutes at 12, a date window at 3, and an IWC calibre in the 69xxx series. Anything that departs from those points is either a different reference or a copy.
Prerequisites
- A digital caliper or a reliable steel ruler
- A 10x loupe
- Bright, diffused light
- Reference photos of a known genuine IW371628
- Permission from the seller to handle the watch
Step-by-step inspection
- Measure the case across the bezel at 3 and 9. Genuine is 41.0 mm; replicas often land between 40.2 and 40.6 mm.
- Weigh the watch head. A steel Portugieser Chronograph on a strap sits near 80 g, and fakes usually run 10 to 20 g lighter.
- Turn the watch over and read the caseback. Genuine engraving is shallow, sharp, and even, with reference and serial set in matching type.
- Compare the subdial centers. They belong at 12 and 6 with a clear gap between them; copies crowd both toward the middle.
- Study the dial print with the loupe. "IWC" and "SCHAFFHAUSEN" should be crisp, with no ink bleed or shadowing.
- Inspect the date window. It should be a clean rectangle with a beveled frame, aligned with the 3 o'clock marker.
- Press the top pusher. The chronograph should start with short, firm travel and no grinding.
- Press the bottom pusher. The hands should fly back to zero in one motion, not creep or stop off-center.
- Wind the crown. Resistance should feel smooth and light, not gritty or loose.
- Tilt the crystal toward a light source. Genuine sapphire shows a faint blue or purple anti-reflective tint, not a heavy mirror coat.
- Check the lugs and spring bars. Genuine lugs are thick with polished top surfaces and brushed flanks.
- Write down the serial and reference from the caseback and compare them with the paperwork.
Movement checks
The IW371628 runs an IWC calibre in the 69xxx family, a cam-switching chronograph built on the Valjoux 7750 architecture. Many replicas use the same base, so a look at the rotor proves little on its own. Judge the decoration instead: perlage on the plates, striped finishing on the rotor, and screws set flush. Stamped or painted finishing is a clear sign of a copy.
Common tells on replicas
- Dial print that thickens at the serifs
- Applied indices that sit off the minute track
- Date numerals that are too wide or too bold
- Caseback text with uneven letter spacing
- Strap hardware with soft, rounded edges
Paperwork and seller checks
Ask for the warranty card, the original invoice, and a clear photo of the caseback. Genuine paperwork lists the reference in the same format stamped on the watch. A seller who will not send a straight-on caseback photo, or who offers no return window, carries more risk than any single cosmetic flaw you might find.