A genuine IWC Portugieser Chronograph reference IW371736 is a 41 mm steel watch with an in-house caliber 69355, a column-wheel chronograph, and a 60-hour power reserve. Fakes of this reference give themselves away in four areas: dial printing, chronograph behavior, case finishing, and caseback engraving. Work through those four in order and most replicas never reach checkout.

Prerequisites

  • Digital calipers that read to 0.01 mm
  • 10x jeweler's loupe or a macro lens for a phone camera
  • Small gram scale
  • Timegrapher, or a watchmaker who owns one
  • Photos of a known genuine IW371736 shot at the same angle and light
  • Seller permission to inspect the caseback and move the chronograph

Genuine IW371736 specs to compare against

  • Case: 41 mm steel, roughly 13 mm thick, 20 mm lug width
  • Movement: IWC caliber 69355, automatic, column wheel, vertical clutch, 46 jewels, 28,800 vph, 60-hour reserve
  • Dial: applied numerals and indices, leaf hands, 30-minute counter at 12, small seconds at 6, date at 3
  • Crystal: sapphire with anti-reflective coating on both faces
  • Water resistance: 30 m
  • Strap: alligator leather with a signed steel pin or folding clasp

How to authenticate an IW371736 step by step

  1. Set the watch on a gram scale and note the weight of the head with the strap removed. A stamped case around a clone movement lands far below a genuine steel head, often 15 to 25 percent lighter.
  2. Measure the case across the 9 and 3 o'clock line with calipers. Genuine width is 41.0 mm, and a case that reads 40.5 mm or 42 mm is wrong.
  3. Measure thickness and lug width the same way. About 13 mm thick with 20 mm lugs is correct.
  4. Study the dial under the loupe. The IWC mark, SCHAFFHAUSEN, CHRONOGRAPH AUTOMATIC, and the small SWISS MADE at 6 should have crisp edges with no ink bleed or silvering.
  5. Compare the applied numerals. Genuine markers sit at one height with polished facets, while fake markers tilt, sit low, or show glue at the base.
  6. Check the subdial rings. The 12 and 6 counters must be centered on the vertical axis with equal gaps to the chapter ring.
  7. Reset the chronograph and watch the central hand. A vertical clutch starts with no jump and returns to 12 exactly. Clone movements jump on start and can land off center.
  8. Time the sweep. 28,800 vph gives eight beats per second, so the small seconds hand moves with a fine step. A 21,600 clone runs at six beats and looks choppy.
  9. Run a timegrapher reading if you can. A serviced 69355 holds a steady rate and healthy amplitude, while a clone drifts between positions.
  10. Turn the watch over and inspect the caseback under magnification. Reference and serial engraving on a genuine piece is fine laser work with matte fill, not deep stamping with raised burrs.
  11. Work the crown and pushers. Genuine pushers have a short, clean travel with an audible click, and the crown winds without grit.
  12. Match the serial on the caseback to the warranty card, the box label, and the booklet. Then ask an IWC boutique or authorized service center to check that serial against their records.

Red flags that need no tools

  • A date digit with the wrong font or a disc that sits slanted in the aperture
  • A rotor that spins freely with a metallic rattle when you tilt the watch
  • Caseback text that spells the reference or the city name wrong
  • A bracelet or strap with no signed clasp or no stitching pattern matching the genuine alligator
  • A warranty card that names a dealer IWC does not list
  • A price that lands far under the current market for a steel Portugieser Chronograph

What replicas get right, and where they stop

Good replicas copy the case silhouette, the dial layout, and the strap color well enough to fool a photo. They fail on the parts you cannot fake cheaply: the movement architecture, the engraved caseback, the crystal coating, and the weight of the head in the hand. If you handle a real IW371736 once, the difference in mass and in the chronograph pusher feel becomes hard to miss.

Buying questions to settle first

Ask whether the seller will allow a watchmaker inspection before payment, whether the movement has ever been serviced, and whether the original box and papers come with it. A seller who refuses an inspection on a reference like this is telling you something. For anyone shopping replica or homage versions of the IW371736 on purpose, the same checklist still works. Judge the case finish, the subdial alignment, the chronograph reset, and the engraving quality, because those four points separate a wearable piece from a throwaway one.