The short answer to the fake IW371784 question: confirm the reference number exists before you inspect a single detail on the watch. My top pick is a reference-first check, run in this order: verify IW371784 against IWC's own catalogue, measure the case and read the crystal, inspect dial printing under a loupe, then review the movement, paperwork and seller. Those four criteria are listed below, each with the details that separate a genuine Portugieser Chronograph from a replica built to imitate one. Run them in sequence and most bad watches fall out at step one.
Step 1: Confirm the reference number exists
A reference number is a factory code, and it is the first thing a counterfeiter has to invent or borrow. IW371784 should resolve, on IWC's model pages or in archived catalogues, to a specific Portugieser Chronograph with a defined case metal, dial colour and calibre. Write down exactly what the maker lists: case diameter, thickness, crystal type, dial layout and movement. Every later check is a comparison against that list, not against a photo you found on a forum.
- Green flag: the seller quotes the full reference and the maker's specification matches the metal and dial on offer.
- Green flag: the number appears in the maker's own material and in independent editorial coverage of the model.
- Red flag: the number appears only on resale listings and replica forums, never on the maker's pages.
- Red flag: the reference changes between messages, or one listing shows watches with different dials and the same number.
Best for: any purchase you have not yet handled in person. Ten minutes here removes most of the risk.
Step 2: Measure the case and read the crystal
Use digital calipers, not a ruler. Measure the case across the bezel at 9 and 3, measure thickness at the caseband, and measure the gap between the lugs. Compare each figure with the manufacturer's stated numbers for that reference. A watch that is half a millimetre oversized or a full millimetre thick is usually a case built around a different movement.
Genuine sapphire with anti-reflective coating on both faces almost disappears over a dark dial, with only a faint tint at a steep angle. Replica crystals often show a grey cast, a strong reflection from a single coated face, or a flat profile where the original is domed.
- Green flag: crisp case edges, even polishing, lugs that taper without a machining line.
- Green flag: a domed crystal that stays legible from an angle.
- Red flag: soft or rounded case edges from over-polishing, or a sharp step where the bezel meets the band.
- Red flag: mineral glass, a milky edge, or reflections that wash out the dial.
Best for: buy-and-hold buyers who care about case integrity and future servicing.
Step 3: Read the dial under magnification
This is where most replicas fail. Under a 10x loupe, the printing on a genuine dial has clean edges and no ink bleed, the applied numerals sit flush with polished bevels, and the leaf hands carry a facet line down the centre that catches light. Subdial hands should reach their markers, and the minute track should be printed with an even weight all the way round.
The Portugieser Chronograph is a no-date watch. A date window at 3 o'clock on a watch sold as IW371784 is a strong sign that the dial belongs to a different model, or to a replica case built around a generic chronograph movement.
- Green flag: correct subdial positions at 12 and 6, sharp railway track, aligned hands at rest.
- Green flag: applied markers with a visible bevel and a flat top.
- Red flag: thick, blobby printing, or a logo that sits too high or too low.
- Red flag: flat stamped hands, a date window, or subdials crowded toward the centre.
Best for: remote buys where the seller can send macro photos or a short video on request.
Step 4: Check the movement, caseback and feel
If the reference has a display back, ask for a clear photo of the movement. Genuine in-house calibres show real Geneva stripes with depth, polished screw heads and a signed rotor. Laser-etched decoration looks printed and flat under a loupe. Ask the seller to start the chronograph, let it run, then reset: the hands should snap back to zero in one movement. Pushers on a genuine watch feel short and crisp, not spongy. A rotor that rattles or a winding action that feels gritty points to a low-cost chronograph base.
- Green flag: a movement photo with real finishing and a serial that matches the paperwork.
- Green flag: an immediate, clean chronograph reset.
- Red flag: a solid back on a reference that should have a display back, or an engraved caseback with shallow, rounded lettering.
- Red flag: refusal to send movement photos or a video of the chronograph running.
Best for: buyers paying close to market rate, where a service bill would erase the saving.
Step 5: Paperwork, price and seller conduct
Boxes and warranty cards are easy to copy, so treat them as supporting evidence, not proof. Check that the serial on the card matches the caseback, that the booklet matches the reference, and that the seller's story about the purchase date fits the production years for that number. On price, compare against established marketplaces for the same reference and condition. A discount far below the going rate is the oldest signal there is.
- Green flag: a return window, escrow or card payment, and a seller who answers specific questions with photos.
- Green flag: a service history from an authorised centre.
- Red flag: wire transfer only, pressure to move fast, or stock photos instead of the actual watch.
- Red flag: a price that sits far under every comparable listing.
Best for: first-time buyers of the reference, who have the least to fall back on if the watch is wrong.
Quick checklist before you pay
- Reference resolves in the maker's catalogue with the same metal and dial.
- Case diameter, thickness and lug gap match the published figures.
- Crystal is domed sapphire with coating on both faces.
- Dial printing is sharp, no date window, subdials at 12 and 6.
- Movement photo shows real finishing and a matching serial.
- Chronograph resets instantly to zero.
- Seller accepts a return window and a traceable payment method.
If a listing fails the first item, stop there. A reference that cannot be confirmed is not a bargain, it is an unfinished question.