The most dependable way to find out whether an IWC Portugieser Chronograph IW371766 is genuine is a hands-on inspection at an IWC service center or an authorized dealer, and that is our top pick for anyone about to spend real money on this reference. We ranked the available verification routes on four criteria: whether the check reaches the movement instead of stopping at the case and dial, what written record you get if a sale later turns sour, the cost and the turnaround time, and whether the method still works when the seller is a private party halfway across the country.

Why the IW371766 Is a Common Counterfeit Target

The Portugieser Chronograph is a clean, symmetrical design with two subdials, applied numerals, and a thin bezel. Clean designs are easier to copy than busy ones, because there are fewer details for a counterfeiter to get wrong. The reference also sells in high numbers, so genuine examples circulate on the secondhand market alongside copies, and buyers often shop from photos alone.

Most reported fakes fail in a handful of predictable places:

  • Subdial spacing that sits slightly too close together or too far apart, a sign of a generic chronograph module instead of the in-house calibre used in current production.
  • Dial printing that looks flat or slightly fuzzy under magnification, especially the fine minute track and the brand signature.
  • Case finishing where the polished and brushed surfaces meet, with soft or wandering transitions rather than a crisp line.
  • Pushers and crown that feel gritty or sit at the wrong height relative to the case band.
  • Caseback engraving that is shallow, uneven in depth, or missing detail around the reference and serial numbers.

Option 1: IWC Service Center or Authorized Dealer

This is the benchmark. A watchmaker opens the case, reads the movement, checks the case and dial against factory records, and can confirm whether the reference and serial numbers belong together.

Pros

  • The movement is examined directly, which no photo-based check can match.
  • You get an opinion from people who handle this reference every week.
  • A service estimate or written note carries real weight in a dispute or a return.

Cons

  • You usually have to ship the watch or travel to a boutique, so it takes time.
  • Some service centers charge an inspection fee, and a full service is a separate cost.
  • It is impractical when the seller still holds the watch and you are only at the negotiation stage.

Best for: any purchase above a few thousand dollars, and any private sale where the paperwork is thin or the story does not add up.

Option 2: Independent Watchmaker With Chronograph Experience

A local watchmaker who services chronographs can do much of the same work: open the case, inspect the movement architecture, check the finishing on the bridges, and time the watch on a machine. Many will do this while you wait.

Pros

  • Fast turnaround and often a modest flat fee.
  • Useful for a first screen before you commit to a factory service.
  • You can watch the inspection happen, which removes a layer of trust.

Cons

  • Not every watchmaker knows this reference well enough to spot a high-grade copy.
  • Written reports vary in quality, and some shops will not put anything in writing.
  • Opening the case adds a small risk of marks if the watchmaker is careless.

Best for: a fast second opinion on a watch you can physically bring in, or a pre-screen before a dealer visit.

Option 3: Seller Documentation and Remote Photo Checks

When the watch is remote, you are limited to what the seller will show you. Ask for sharp, well-lit images of the dial at an angle, the caseback engraving, the clasp, and the movement if the caseback is a display type. Ask for a short video with the chronograph running and resetting to zero.

Pros

  • Costs nothing and can rule out obvious fakes in minutes.
  • Complete sets with matching box, booklets, and dated warranty card are harder to assemble around a copy.
  • You can compare details side by side with published reference photos.

Cons

  • Photos hide movement problems and can be retouched or borrowed from another listing.
  • A genuine box and papers can be paired with a counterfeit watch.
  • No written authentication means little recourse if the watch turns out to be fake.

Best for: filtering listings before you spend money on an in-person check, never as the final word.

Quick Checklist Before You Commit

  1. Match the reference and serial numbers on the caseback to the paperwork.
  2. Compare subdial spacing and date placement against official reference images of the IW371766.
  3. Look at the dial under magnification for the minute track and signature.
  4. Run the chronograph: start, stop, and reset should feel crisp and return cleanly to zero.
  5. Confirm the service history if the seller claims one.
  6. Pay through a method that allows a dispute, and keep every message.

Bottom Line

Use the seller documentation route to filter candidates, an independent watchmaker to screen a watch you can hold, and an IWC service center or authorized dealer before money changes hands on anything expensive. A counterfeit IW371766 is built to survive a glance at a photo. It is far harder to survive a watchmaker with a loupe, a timing machine, and the caseback off.