The single most reliable check on a fake IW371645 is the movement seen through the display back. A genuine Portugieser Chronograph from the 3716 generation runs an in-house IWC automatic chronograph calibre with a column wheel and roughly two days of power reserve, and counterfeiters rarely copy that architecture. Dial printing, case finishing, pusher feel, strap hardware, paperwork and price all matter, but they are secondary filters. Judge any candidate on five criteria: movement, dial and subdials, case and crown, hardware and documents, and whether the numbers on the watch match the numbers on the papers. IW371645 sits inside IWC's 3716 reference block, so pull the official spec sheet for that exact reference before you compare anything, because dial and case variants change from year to year.
1. The display back and the movement
Ask for a live video through the case back, not a stock photo. Genuine 3716-generation watches show a self-winding IWC calibre with recognisable finishing, a signed rotor, and chronograph pushers that start, stop and reset with a light, even action. A counterfeit usually hides a Valjoux 7750 derivative, a Seagull chronograph, or a decorated Asian movement under a printed rotor plate.
What this check catches
- Wrong movement family, a giveaway that no amount of dial work can fix
- Wrong beat rate: a watch running at 21,600 vph instead of the modern 28,800 vph
- Rotor engraving that is shallow, off-centre or the wrong typeface
- Pushers that jump, stick or feel gritty on reset
Where it falls short
- Frankenwatches with a genuine movement in a fake case still pass
- Stock photography hides everything; you need live footage
- A service replacement part is not proof of a fake, so check the service history
Use it when: you are buying online from a private seller and can request video of the watch running with the back visible.
2. Dial printing, subdials and the date
Compare macro photos of the candidate against IWC's own photography for the exact variant. On a fake, the tells cluster in small places: text weight and letter spacing, the depth of the subdial rings, the alignment of the date aperture, and applied markers that sit flush when they should not or float when they should sit tight.
What this check catches
- Muddy or doubled printing on the brand and text lines
- Subdials spaced slightly wrong, or with flat rather than recessed rings
- Date wheels with the wrong font, wrong colour or misaligned numerals
- Hands with the wrong length or a poorly finished sweep seconds hand
Where it falls short
- Good replicas have excellent dials, so this alone decides nothing
- Legitimate dial variants exist across production years
- Phone photos distort print weight and can make a real dial look wrong
Use it when: you are shortlisting from listing photos and need to eliminate obvious mismatches fast.
3. Case, crown and pushers
Run a fingernail along the boundary between polished and brushed surfaces. On a genuine case the transition is crisp and consistent; on a fake it is usually rounded, wavy or uneven from lug to lug. Check the crown for a clean, deep logo and count the threads and gasket seat if you can see them.
What this check catches
- Sloppy polishing transitions and soft lug edges
- Shallow or fuzzy engraving on the case back
- Pushers of the wrong diameter or with a rough, unfinished cap
- Case proportions that differ by a fraction of a millimetre from the published spec
Where it falls short
- A polished and refinished genuine case can look worse than a new fake
- Small dimensional differences are hard to judge without calipers
Use it when: you have the watch in hand, which makes this the cheapest and fastest filter available.
4. Strap, clasp, box and papers
Boxes, booklets and warranty cards are the easiest thing in the world to reproduce, so treat them as packaging rather than proof. Look at stitching density on the strap, the engraving depth on the buckle or folding clasp, and whether the inner lining and keeper match the reference.
What this check catches
- Generic straps with uneven stitching and no signed hardware
- Clasp engraving that is laser-light rather than stamped deep
- Paperwork with spelling errors, wrong reference codes or mismatched serial numbers
Where it falls short
- Genuine watches are often sold loose, without box or papers
- Full sets are widely counterfeited and prove nothing on their own
Use it when: the seller leans on a full set to justify a premium, which is exactly when the paperwork deserves scrutiny.
5. Reference number and price sanity
Genuine steel Portugieser Chronographs trade in the thousands of US dollars on the secondary market, and a full set adds a premium. A watch described as new and complete at a small fraction of that range is a replica or a counterfeit, not a find. Separately, confirm the listed reference matches the watch itself: sellers frequently label an older-generation case as IW371645 to make a listing look current.
What this check catches
- Reference codes that do not match the case, dial layout or movement
- Case and movement numbers that contradict the documentation
- Prices that assume a buyer will not compare against the market
Where it falls short
- Genuine bargains do exist from motivated sellers or at auction
- Market ranges vary with condition, age and completeness
Use it when: the deal looks unusually strong, which is the moment to slow down rather than speed up.
Which check to use in your situation
If you want a genuine watch, gate everything on the movement: no live movement footage, no purchase. Buy from a seller with service records, and budget for a service on any watch over a decade old. If you already own a suspect IW371645, take it to an independent watchmaker rather than the person who sold it. If you knowingly want a replica, buy only from a seller who describes it as a replica and states the movement, case size, crystal and water resistance, and pay replica money. Passing a counterfeit off as genuine is fraud in the US and most other markets, and shipments can be seized by customs, so keep the description honest at every step.