The short answer
A fake IW371429 is a counterfeit copy of the IWC Portugieser Chronograph. A genuine example is a 40.9 mm steel case with two subdials, a chronograph calibre built on the Valjoux 7750 base, and a sapphire display back. Copies match the outline and miss the details: soft dial print, misaligned subdials, a blank movement, and a caseback with the wrong engraving. Check the movement first. If the seller will not show it, walk away.
What the genuine reference should show
Know the target before you judge any watch. The Portugieser Chronograph line runs a 40.9 mm case with feuille hands, applied numerals, a railroad minute track, a 30 minute counter at 12 o'clock, and small seconds at 6 o'clock. The dial carries no date. Water resistance is rated for splash contact, not swimming. The caseback holds the reference number and a serial, and the movement inside has IWC finishing and a signed rotor.
What you need
- A 10x loupe
- Digital calipers
- A reference photo of the dial and caseback
- The watch in hand, or clear photos from the seller
How to inspect a suspect watch
Work through these steps in order. Stop when one fails.
- Set the watch on a flat surface and measure the case with calipers, then compare the diameter and thickness with the published spec.
- Put the loupe on the dial print. Genuine IWC lettering has sharp edges and even stroke weight.
- Compare the subdial centers against the printed tracks. Both subdials should sit on the vertical axis and the hands should reach the track.
- Press each pusher. A 7750 based chronograph starts with a firm click and the reset snaps back to zero in one motion.
- Turn the watch over and read the movement through the display back. Look for the IWC engraving, rotor finish, and polished screws. Coarse finishing ends the inspection.
- Compare the caseback engraving with your reference photo. The reference number, serial, and font weight must match.
- Check the strap and buckle. Genuine alligator and a signed steel pin buckle feel different from printed leather and a cast buckle.
Red flags that end the conversation
- A price far below the pre-owned market with a no returns policy attached.
- Photos that avoid the caseback, the movement, or the crown side.
- A date window on a two register dial.
- A calibre number that does not match the reference.
- Box and papers printed with a serial that does not match the case.
If you want a replica on purpose
Many buyers who search for a fake IW371429 want a replica, not a genuine watch. The same checks apply in reverse. A good copy should match the case size, the dial layout, and the subdial function, and the listing should state which movement it uses. Sellers who hide the movement spec are hiding the weakest part of the build. Ask for a photo of the caseback and a video of the running chronograph before you pay.