Short answer: the check that settles a fake IW371752 fastest is the movement, confirmed by a clear photo with the caseback removed or by a watchmaker on a bench. Genuine IWC Portugieser Chronograph watches in this family carry either IWC's reworked 79350 calibre or the newer in-house 69000-series chronograph, while the copies that circulate run stock 7750-pattern or Asian chronograph movements whose finishing does not survive a loupe. That is our top pick among the checks below because it is the hardest thing for a counterfeiter to reproduce. The remaining criteria (case geometry, dial printing, subdial layout, crown and pusher feel, strap hardware, and paperwork) matter because they let you reject a bad watch in under a minute, before you ever ask a seller to open a case.
Check the reference number before anything else
IWC reference numbers combine a family number with suffixes that encode case metal, dial and strap combination. A watch in the 3717 group belongs to the Portugieser Chronograph family, so a listing that files an IW371752 under Pilot's Watch or Ingenieur is already wrong. Verify the exact configuration against IWC's own reference data rather than a marketplace title, because sellers frequently relabel watches using borrowed stock photos.
Pros
- Costs nothing and takes seconds.
- Catches mislabeled listings and wrong-family watches immediately.
- Narrows the correct case metal, dial color and strap for the watch you are comparing against.
Cons
- Suffix codes vary across production years and markets, so a single mismatch is not proof of a fake.
- Many sellers copy the wrong reference out of carelessness rather than fraud.
Best for: the first thirty seconds of screening any online listing, before you study the photos in detail.
Movement and caseback: the decisive test
Ask for a sharp photo of the movement and a short video showing the chronograph starting, stopping and resetting. On a genuine watch the rotor engraving is cut deep and evenly, screw slots are clean and undamaged, and the decoration under the rotor is applied with consistent circular graining. Copies usually show shallow laser engraving, uneven brushing, and a rotor that sits too close to the bridges. Confirm also that the small running-seconds dial sits at 6 o'clock and the elapsed-minute counter at 12, which is the layout of this Portugieser Chronograph family. A stock 7750 base places running seconds at 9, and a watch presenting that layout under this reference is either a different model or a conversion.
Pros
- Very hard to fake at 1:1, so the result is close to definitive.
- Video of the pusher action reveals sticky resets and slow engagement.
Cons
- Requires the seller to open the watch, and some will refuse.
- A service caseback or a swapped movement can fool a photo.
- Some sellers send movement photos that belong to a different watch.
Best for: every remote purchase and any deal above the amount you would be willing to write off.
Dial printing, hands and subdials
Look for dished or recessed subdials, applied indices with crisp polished facets, and lettering that stays sharp at macro distance. Common faults on copies include flat subdial surfaces, lume that bleeds past the plots, indices that do not sit parallel to each other, and font weight that is heavier or lighter than the reference dial. Leaf-shaped hands should be polished along the bevel with a clean edge line under a loupe.
Pros
- Visible in ordinary photos with no tools and no seller cooperation.
- Fast way to eliminate the obvious low-tier copies.
Cons
- Good lighting and a macro shot can flatter a poor dial.
- Dial variants differ by reference, so you must compare against the correct one.
Best for: listings where the seller will not open the case or provide movement shots.
Case, crystal, crown and pushers
Genuine cases mix brushed flanks with polished bevels and have lugs that taper cleanly into the strap. The crown carries fine engraving, and the pushers travel a short, crisp distance with no grit. The sapphire should show a faint blue or purple anti-reflective tint at an angle. Hand the watch over: a case that feels light, tinny or sharp along the lug edges is worth a second look.
Pros
- Hand feel catches things photos cannot show.
- Pusher and crown action is difficult to replicate convincingly.
Cons
- Requires in-person inspection.
- A correctly refinished vintage case can look different from factory condition without being fake.
Best for: private sales, pawn shops and any face-to-face meeting.
Strap, buckle and hardware
Factory leather is thick, evenly stitched and finished at the edges. Folding clasps and pin buckles carry clean engraving with consistent depth. Copies often ship thin leather with uneven edge paint and a clasp whose markings are stamped rather than cut. On a used watch, a replacement strap is normal and not a red flag on its own.
Pros
- Quick to judge in hand and cheap to replace if you are wrong.
- Wrong-brand hardware is a strong signal of a parts-built watch.
Cons
- Straps are consumables, so an aftermarket strap proves nothing about the watch.
Best for: watch-only listings where box and papers are absent.
Price, paperwork and provenance
If a complete watch is offered far below the going rate for that reference in that condition, assume something is wrong until the movement proves otherwise. Boxes and papers can be purchased separately, so treat them as supporting evidence rather than proof. Ask for the original invoice, service records and a seller history that predates the listing.
Pros
- Pricing gaps expose problem watches faster than any visual check.
- Service paperwork from an authorized center is strong corroboration.
Cons
- Papers can be forged or sourced separately from the watch.
- Honest sellers sometimes lose documents, so absence alone is not conclusive.
Best for: closing a deal and for setting your own price ceiling.
If you are shopping for a replica instead
Buyers who want the look of this reference without the genuine outlay should judge sellers on evidence, not adjectives. Ask for dated QC photos of the actual watch, confirm the subdial layout matches the 6 and 12 arrangement, check stated case thickness and crystal coating, and walk away from anyone who cannot show the movement. Expect decoration on the rotor and caseback engraving to be the weakest areas, and price the watch as a replica rather than as an investment.
Best for: buyers who want the design language of the Portugieser Chronograph and accept that the movement will never match the genuine calibre.