A fake IW371490 gives itself away in measurable details, not in a gut feeling. Genuine IWC Portugieser Chronographs in this reference family run a 40.9 mm case, a 30-minute totalizer at 12 o'clock, running seconds at 6, a date window at 3, and calibre 79350 inside. Measure the case, read the dial under magnification, check the caseback engraving, and identify the movement. Any of those four checks can settle the question on its own.
What the reference number tells you
IW371490 belongs to the Portugieser Chronograph line, the 3714 family that IWC has produced in many dial and metal versions since the late 1990s. Counterfeiters target this family because the design is simple and popular. Most fakes copy the overall look while missing proportions, finishing and the chronograph module underneath.
Prerequisites
- Digital caliper that reads to 0.01 mm
- 10x jeweler's loupe and a bright, diffused light
- Photos of a known genuine IW371490 for side-by-side comparison
- Caseback opening tool, or a local watchmaker willing to open it
- Kitchen scale accurate to 1 gram
Step-by-step checks
- Measure the case across 3 and 9 with the caliper. A genuine example sits at about 40.9 mm wide and roughly 12.3 mm thick. Counterfeits often run 0.5 to 1.5 mm off, and the lugs measure 20 mm apart on the real watch.
- Weigh the watch on the scale. A stainless 3714 head with a leather strap lands in a narrow band. A fake with a plated brass case feels light in the hand and reads low on the scale.
- Confirm the subdial layout. The 30-minute chronograph counter sits at 12, small seconds at 6, date at 3. On fakes the counters are spaced wrong, the hands are too short, or the subdial rings are printed instead of recessed.
- Examine the dial print at 10x. Genuine lettering is sharp with even spacing and no bleed into the lacquer. Look at the brand name, the automatic line, and the track print around the outer edge.
- Study the date aperture. The window edge should be crisp and the numerals should match IWC's font, with a flat top on the 1 and a straight leg on the 4. Fake date wheels use generic typefaces and the cutout is often too wide or set too low.
- Read the caseback engravings. Reference, case number and serial should be deep, crisp and evenly aligned. Shallow laser etching with rounded edges points to a fake case.
- Open the back and identify the movement. Calibre 79350 is a Valjoux 7750 base with 31 jewels, 28,800 vibrations per hour and about 44 hours of reserve. Look for the IWC rotor engraving, Geneva stripes and circular graining on the bridges.
- Work the chronograph from a dead stop. Push start, let it run, push stop, then reset. The hands should snap back to zero together. Mushy pushers or hands that drift off zero are a strong sign of a cheap module.
- Inspect the crown and pushers. The crown carries the IWC logo in relief, sits flush against the case, and winds with light resistance. Polished, poorly fitted pushers with visible gaps are common on replicas.
- Check the crystal under a lamp. Genuine sapphire shows a faint blue anti-reflective tint and stays clear. Mineral glass looks flat, and acrylic shows fine scratches after light wear.
- Review the strap, clasp and buckle. Signed hardware, dense stitching and even alligator scaling are the norm. Fakes use loose stitching, thin hardware and stamped logos with no depth.
- Cross-check the serial with IWC service. Send the case number and serial to official IWC customer service and ask for a record match. Papers and boxes can be printed convincingly, so verify the numbers against the watch, not the packaging.
Red flags that decide it fast
- Subdial hands that do not reset to 12
- Caseback engravings you can rub with a fingernail
- A movement without IWC finishing or rotor markings
- Dial print that looks blurry at arm's length
- A serial that does not match the movement number
- A price far below current market for a steel 3714
When to hand it to a professional
If the case measures correctly but the movement is unmarked or the serial does not come back from IWC, stop and take the watch to an independent watchmaker. A trained eye can confirm the base calibre, the finish quality and any swapped parts in minutes. Buying without that confirmation is the fastest way to end up with a fake IW371490 that looks right in photos and wrong on the wrist.