Quick answer
A genuine IW371741 is a stainless steel IWC Portugieser Chronograph with an in-house IWC chronograph movement behind a sapphire display back, sharp applied indices, and a signed crown and pushers. Most fakes fail on three points: the movement, the dial printing, and the case back engraving. Check those three before you spend time on anything else.
Prerequisites
- A 10x loupe or a phone macro lens
- A bright, angled light source
- Calipers if you can measure the case
- Full resolution seller photos, plus the reference and serial numbers
- IWC's published reference data for the 3717 Portugieser family
How to check an IW371741 for authenticity
- Measure the case diameter and thickness with calipers and compare the numbers to the published spec for the reference.
- Photograph the dial straight on and study it at 10x. Genuine printing sits crisp and raised, with clean edges on every numeral and the IWC logo.
- Trace each chronograph hand to its subdial and confirm the hand lengths and stack heights match the reference.
- Turn the watch over and inspect the movement through the display back. You are looking for IWC's in-house chronograph architecture, not a generic third party calibre dropped into the case.
- Read the rotor engraving. The IWC marking and the Probus Scafusia motto should be sharp, evenly spaced, and cut into the metal.
- Press the pushers and start the chronograph. Genuine column wheel actuation feels firm and clean, and the reset snaps to zero in one motion.
- Inspect the case back text with the loupe. Reference and serial numbers on a real watch are cut deep, evenly aligned, and consistent with IWC's engraving style.
- Check the crown. It should carry the IWC marking and thread smoothly with no wobble.
- Examine the bracelet or strap hardware. Clasp stamps, spring bar fit, and link finishing are where cheaper copies give themselves away.
- Ask for service paperwork, an IWC service invoice, or a movement service record before you buy.
- Have a watchmaker open the case and time the movement. A genuine IWC chronograph runs at 4 Hz and holds steady rate in several positions.
Red flags
- A price far below the normal secondary market range
- A seller who refuses macro photos of the movement or the case back
- Blurry or bleeding dial printing under magnification
- A solid case back on a reference that should have a display back
- Serial number fonts that differ in size or spacing from IWC's standard
- Chronograph pushers that feel spongy or reset in two steps
Why this matters
The IW371741 sits in the Portugieser Chronograph line, one of IWC's most copied designs. Because the case shape and dial layout are simple to reproduce, the movement is the strongest proof of authenticity. A counterfeit rarely carries a column wheel chronograph with proper finishing, and it almost never keeps time to IWC's tolerances. When the movement checks out, the dial and case back checks usually confirm what you already suspect. When the movement does not check out, walk away no matter how good the price looks.