Short answer
Most fake IW371740 watches fall apart at the details IWC machines to a tight tolerance: the caseback engraving, the dial print, the date font, and the movement. If the reference stamped on the back does not match the dial layout in front of you, or the engraving looks shallow and laser-etched, treat it as a copy. A genuine one can be confirmed by IWC or an authorized dealer from the serial number.
What the reference number tells you
IWC writes references in the form IW plus six digits. The first four digits identify the model family, and the last two point to a case and strap variant. So IW3717 and IW371740 are related, but they are not interchangeable in a listing. A watch described as one reference while carrying dial details from another is a strong signal something is off.
Fakes in this family often carry a reference that was never produced in that combination, or a serial that sits outside the range the brand used for that year. Neither is visible in a thumbnail photo, which is exactly why so many listings hide the caseback.
Where copies give themselves away
- Caseback engraving: real stamps have depth and clean edges. Fakes look printed, faint, or too wide.
- Dial print: the brand name and the Schaffhausen line should stay sharp under a loupe. Copies thicken and blur the letters.
- Subdial rings: check the spacing to the center and how the rings are printed. Flat, fuzzy rings are a tell.
- Date wheel: numeral shape and window position. A generic date disc never matches the original font.
- Crown and pushers: thread quality, the action of the pushers, and engraving on the crown head.
- Movement: rotor engraving, bridge finishing, and beat rate. A timegrapher exposes most copies in seconds.
- Case finishing: brushing direction, polished bevels, and how the lugs flow into the case.
Why this reference gets copied
Chronograph references with clean dials and a well-known name are the easiest to move in volume. The case shape is simple enough to reproduce on a CNC machine, and the dial carries few elements, so a decent copy can pass at arm's length. The gap shows up under magnification and on a timing machine, which is where the money actually goes in a good build.
If you are buying a replica instead
Judge it on the same criteria. A proper 1:1 build should match the case diameter and thickness, use sapphire with a real anti-reflective coating, print the dial cleanly, and run a movement that starts, stops and resets the chronograph without the seconds hand jumping. Ask for photos of the actual watch with the caseback open, not catalog images. Cheap copies cut corners on the crystal, the crown threads and the bracelet end links, and those are the parts you touch every single day.
How to verify before you pay
- Photograph the caseback, dial and crown, then compare the reference and serial against brand records or a dealer's database.
- Request a movement photo or a short video of the chronograph running and resetting.
- Check the date font and the subdial ring printing under magnification.
- Weigh the watch. A hollow case and a stamped bracelet show up on a kitchen scale.
- Buy from a seller who accepts returns, and get the return window in writing.
The bottom line
Reference checks beat gut feeling. Match the number on the back to the dial in front, look at the printing and the movement, and you will know within a minute whether you are holding a fake IW371740 or the real thing.