The short answer: the fake IW371490 question is settled fastest by the movement, seen through the caseback. A counterfeiter can copy dial printing and case finishing to a point where photos look convincing, but the gear train, rotor engraving, and finishing under a loupe are the hardest details to reproduce at a fake price. Our top pick is therefore the movement check, followed by dial printing, case and crown details, and finally paperwork and seller story. Run them in that order. Each check catches a different class of fake, and none of them proves authenticity alone.
What the reference is supposed to be
IW371490 sits in the IWC Portugieser Chronograph family, a line built around a slim round case, twin subdials, and a clean, readable dial. Production years matter here. Earlier examples in the 3714 family carry caliber 79350, a modified Valjoux 7750 base. Later 41 mm references moved to the in-house 69355. Before you judge any watch, confirm which caliber the reference and production year should carry. A seller who cannot tell you that is not a seller worth negotiating with.
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Check 1: Dial printing and subdial layout
Print quality is the cheapest thing to inspect and the most common place fakes slip. Look at the printing under magnification, not on a phone screen at arm's length.
Catches
- Text that sits slightly off center or drifts on a curve
- Subdial spacing that looks compressed or pushed toward the edges
- Applied markers with visible glue or uneven seating
- Hands with flat, painted finishes where the real part is polished or faceted
Misses
- High tier fakes with correct printing but a wrong movement
- Re-dialed genuine watches, which pass a printing check by definition
Use it when: you are screening a listing from photos and need a fast reason to walk away.
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Check 2: Case, crown, and pushers
Case geometry is where mid tier replicas fall apart. The Portugieser case has a specific profile: a thin bezel, a stepped caseband, and lugs that curve in a particular way. Ask for a straight-on side shot and a straight-on caseback shot. Then ask for a macro of the crown. The crown engraving should be crisp and centered, and the pushers should operate with a firm, defined click rather than a soft mush.
Catches
- Cases that are too thick, a common tell on chronograph replicas
- Soft or shallow crown engraving
- Lugs with sharp, unfinished inner edges
Misses
- Genuine watches that were polished hard and lost their original edges
- Fakes built on genuine cases, which are rare but exist
Use it when: you have good photos and want a second opinion before paying for an inspection.
Check 3: Movement and caseback
This is the check that actually answers the question. On an exhibition caseback, compare what you see to the caliber the reference should carry. Look for the rotor engraving, the finish on the bridges, and the shape of the regulating system. Fake chronographs often show a decorated industrial movement with plating that looks applied rather than finished. If the caseback is solid, move the check to the inside of the caseback and the reference and serial stamping, which should be even and clean.
Catches
- Wrong caliber for the reference or production year
- Decorative plates hiding a different base movement
- Stamped reference numbers that do not match the dial variant
Misses
- Nothing much, if the photo is sharp and lit well. This is the strongest single check you have.
Use it when: the deal is close to done and you need a decision. Insist on a sharp macro of the movement before money moves.
Check 4: Paperwork and seller story
Papers are easy to fake, so treat them as a supporting signal rather than proof. What matters more is whether the story holds together: the reference on the card, the reference on the caseback, and the dial variant should all agree. Ask when the watch was last serviced and who did the work. A seller with a service invoice from a known watchmaker is a different risk profile from a seller with a box and a vague story.
Catches
- Mismatched reference numbers between card and case
- Sellers who avoid service questions or push for a fast sale
- Prices that sit far under the market range for that reference and condition
Misses
- Genuine watches sold without papers, which is common and not automatically a problem
Use it when: you are choosing between two watches that both passed the physical checks.
If you are shopping a replica on purpose
Plenty of people search this reference because they want a replica, not because they fear one. The same checks apply, just pointed at a different question: which tier of replica are you being sold?
Pros of buying a replica Portugieser
- You get the dial layout and case profile at a fraction of the genuine cost
- Parts and service are cheap, so a daily wearer carries less anxiety
- Higher tier replicas now copy the case proportions closely
Cons
- The movement is never the real thing, so the caseback check always fails
- Water resistance is a claim, not a guarantee, on most replicas
- Resale is close to zero and service support is informal
Best for: buyers who want the look for casual wear and accept that the movement is a copy. If you want a watch to pass an inspection, this is the wrong category.
Verdict: order of operations
- Confirm the caliber the reference should carry.
- Get a sharp movement macro and compare.
- Screen the dial and case on photos.
- Reconcile the paperwork and the seller story last.
If the movement matches, the dial is crisp, the case has the right thickness, and the story lines up, you are looking at a genuine watch or an unusually well built fake. At that point, pay for an inspection by a watchmaker who handles IWC. It is the cheapest insurance in this hobby.