The check that settles a fake IW371734 is the movement, viewed together with the caseback engraving. Dial printing, polishing, and hand shape can now be copied closely enough to survive a photo, so they rank below the parts a replica maker cannot reproduce at cost: an IWC-manufactured calibre and reference-correct engraving inside the case. The sections below are ordered by how decisive each check is, with the trade-offs for each and a note on when to use it.
Reference context before you compare anything
IW371734 sits inside IWC's Portugieser Chronograph range, a line built around a two-register layout, applied numerals, leaf hands, and a railway-track minute ring. Because IWC has issued the Portugieser Chronograph across several reference blocks and many dial and case-metal variants, confirm the exact configuration of this reference through IWC's own reference lookup before you judge any single watch. A genuine example must match its documented case metal, dial colour, strap or bracelet, and movement. Comparing a watch to a photo of a different variant is the most common cause of a false alarm.
1. The movement check
This is the top pick and the only test that is close to conclusive. Recent Portugieser Chronograph references use an IWC-manufactured automatic chronograph calibre with a column wheel, roughly 46 hours of power reserve, and a two-register layout. Replica movements are usually third-party chronograph blanks, sometimes with a decorative plate on top. Under a loupe, look for the correct calibre number, the finish on the bridges, the shape of the column wheel and levers, and the rotor engraving.
Pros
- Replica makers cannot match an in-house calibre at replica prices, so a movement mismatch ends the question.
- You can see the chronograph actuation feel, which is crisp on a column wheel and vague on many blanks.
Cons
- It requires opening the caseback, which a watchmaker should do, and which can affect a factory warranty on a new watch.
- A photo of a movement is easy to fake, so only trust an inspection you or a professional performed in person.
Use it when: the amount at stake is meaningful and you can get the watch to a watchmaker before paying in full.
2. Caseback engraving and reference stamping
Genuine IWC casebacks carry crisp, deep engraving with consistent letter spacing and the reference number stamped in a defined place. Replicas often show shallow laser etching, soft edges, or a reference that does not match the dial and movement inside. Check the serial and reference together, and check that the engraving style matches other examples of the same reference block rather than a generic Portugieser photo.
Pros
- Visible with a loupe and a good light, no disassembly needed.
- Cheap and fast to check on a seller's own photos before you commit.
Cons
- High-tier replicas have improved here, so a clean caseback alone proves nothing.
Use it when: you are screening listings remotely and want to eliminate obvious fakes early.
3. Dial, hands, and subdial layout
Look at the small seconds at 6 and the chronograph counter at 12, the date aperture at 3 on versions that have one, and the printing weight of the text. Genuine dials have flat, evenly applied printing, correctly proportioned numerals, and hands that are polished on the bevels and brushed on the flats. Replicas typically show slightly thick printing, numerals that sit a fraction high or low, and hands with a softer edge.
Pros
- You can assess it from clear macro photos without touching the watch.
- Errors here are common in mid-tier replicas.
Cons
- Strong replicas pass this check, and lighting in photos hides a lot.
Use it when: you are comparing several candidates and need a quick shortlist.
4. Case, lugs, and finishing
Run a fingernail along the lug edges and the caseband. Genuine cases have a consistent transition between polished and brushed surfaces, with sharp, defined lines. Replicas often round off those transitions or polish areas that should be brushed. Case thickness is worth measuring against the documented figure for the reference.
Pros
- Catches many replicas that pass the dial check.
- Needs only calipers and your hands.
Cons
- Subjective without a known-genuine example beside it.
Use it when: the watch is in front of you and the movement check is not possible.
5. Papers, box, and service history
A reference-correct card, matching serial, and a documented service record add weight, but paperwork is the easiest thing to fake. Treat papers as supporting evidence only, never as the deciding factor.
Pros
- Confirms the watch's claimed identity and history when the documents are genuine.
Cons
- Printing and packaging are widely copied, so documents can give false confidence.
Use it when: every other check has already passed.
Which check fits your situation
- Buying remotely from a private seller: start with caseback engraving and dial macro photos, then insist on a movement photo taken with the watch in hand and a timestamp.
- Buying in person: book a watchmaker inspection and make payment conditional on it.
- You already own the watch: have the movement and caseback checked once by a professional and keep the report.
- You are comparing replica tiers: accept that dial and case finishing can be close, and judge a replica on what it claims to be, not on whether it passes as genuine.
Quick checklist
- Confirm the exact IW371734 configuration from the manufacturer before comparing.
- Check the movement calibre number, finish, and rotor engraving.
- Check caseback engraving depth, spelling, and reference stamping.
- Check printing weight, numeral placement, and hand finishing.
- Measure case thickness and inspect the lug transitions.
- Treat papers as the last item, not the first.