The fastest way to judge a suspected fake IW371645 is a three-way cross-check: the caseback engraving and reference format, the movement seen through a display back (if that reference has one), and the dial layout compared against IWC's own reference listing. Those three details are the most expensive to copy well, so they catch the largest share of replicas. Everything else, meaning the strap, buckle, box, papers and price, is supporting evidence rather than proof. This guide runs through each check in the order worth doing them, notes where each check fails, and closes with which buying option suits which kind of buyer.
One reference note first. IW371645 sits inside IWC's 3716 Portugieser Chronograph family, a group that spans several releases sharing a case size while differing in dial color, case metal and movement generation. Pull the exact reference page for IW371645 from IWC before you compare, because replica sellers routinely mix details from different 3716 releases into one watch, and a spec sheet copied from the wrong sibling reference will make you doubt a genuine example.
Check 1: Caseback Engraving and Reference Format
Genuine casebacks in this family engrave the reference with the IW prefix, a case number and a serial, all cut to consistent depth with even letter spacing. Replicas often show laser-etched text with rounded edges, drifting spacing, or a mangled reference such as 3716-45 or IW3716 45. Font weight on the reference line usually differs from the serial line on fakes.
Pros
- Needs no tools and works from a photo listing or a face-to-face meeting.
- Catches budget and mid-tier replicas immediately, since engraving depth is hard to fake cheaply.
Cons
- Top replicas use real engraved casebacks and can match the font closely.
- Service refinishing on a genuine watch can soften engraving and set off a false alarm.
Best for: a first-pass screen before you spend time on anything else.
Check 2: Movement and Display Back Configuration
Confirm which back the exact reference should have, because some 3716 watches show the movement and others are closed. If a display back is correct, inspect the rotor engraving, bridge shapes, Geneva stripes, perlage and the column wheel. Replicas commonly hide a generic chronograph movement behind a decorated plate or a rotor carrying the wrong text. Wind and run the chronograph: start, stop and reset should feel crisp with a defined detent at each pusher press.
Pros
- Movement architecture cannot be faked as cheaply as dial printing.
- Pusher feel and reset snap are difficult to imitate on a modified base caliber.
Cons
- Requires macro photos or opening the case, which many sellers refuse.
- A genuine watch with a factory replacement movement still reads as genuine here.
Best for: the deciding check on any watch priced close to market.
Check 3: Dial Layout, Subdials and Date Window
Measure subdial spacing and date window position rather than eyeballing them. Check applied indices for sharp edges and correct height, leaf-shaped hands for finish, and printed text for clean edges under magnification. This is where fantasy builds show up, meaning watches assembled from parts of different references.
Pros
- Visible in most listing photos, so it works remotely.
- Exposes mismatched part combinations that no single reference ever shipped with.
Cons
- Aftermarket dials exist and can look correct at a glance.
- Filters, glare and low-resolution photos hide the flaws you need to see.
Best for: remote screening before you request movement photos.
Check 4: Case Finish, Weight and Crystal
Look at chamfer consistency along the lugs, brushing direction, and how the sapphire behaves under angled light. A coated crystal on a genuine watch suppresses reflections in a way most replicas do not replicate.
Pros
- Hand feel is fast and hard to fake on the spot.
- Crystal coating is a reliable tell in person.
Cons
- Subjective without a known-good example beside it.
- Polishing and strap choice change weight and finish impressions.
Best for: in-person inspections, where photos are not enough.
Check 5: Strap, Buckle, Box and Papers
Check buckle engraving depth and strap stitching density, then treat the box and papers as a separate question. Papers can be verified against the serial through IWC, and that verification matters far more than whether a box is present.
Pros
- Serial verification with IWC is the strongest single piece of documentation you can get.
- Buckle and strap details are easy to compare side by side.
Cons
- Boxes and paper sets are widely copied and prove nothing alone.
- Straps are consumables, so a wrong strap on a genuine watch is normal.
Best for: confirming provenance after the watch itself passes inspection.
Check 6: Price and Seller Signals
A price well below the going rate for a genuine 3716 reference is the oldest warning sign there is. Ask how the seller acquired the watch, request the serial, and check whether returns are allowed.
Pros
- Costs nothing and screens out most scams before contact.
- Seller history and return policy reveal more than any single photo.
Cons
- Genuine watches do sell low in estate or distressed sales.
- A high asking price guarantees nothing about authenticity.
Best for: the last filter before you commit money.
Buying Options and Who Each One Suits
Genuine, from a dealer or through IWC service
- Pros: serviceable, documented, holds value, no legal exposure.
- Cons: highest cost, and older references may need a service soon after purchase.
High-end replica
- Pros: closest visual match, wearable daily, far cheaper than genuine.
- Cons: no manufacturer service, near-zero resale, possible seizure at import, and illegal to sell as genuine anywhere in the US.
Budget replica
- Pros: lowest entry cost if you only want the silhouette.
- Cons: obvious dial and caseback flaws, unreliable chronograph function.
Use-case recommendation: if you want a watch to wear and eventually resell, buy genuine and verify the serial. If you want the look at low cost and accept no service support, a high-end replica is the version most buyers in that position choose. Skip budget replicas if the chronograph function matters to you, because that is the first thing to fail.
Quick Verification Checklist
- Match the reference number to IWC's own listing, including back type.
- Inspect engraving depth, spacing and the IW prefix on the caseback.
- Photograph or view the movement, rotor and column wheel if a display back is correct.
- Measure subdial and date positions against the reference photos.
- Request the serial and confirm it with IWC before paying.
- Compare the asking price with current market listings for the same reference.
Work the checks in order and stop at the first hard failure. A single confirmed mismatch on engraving or movement settles the question faster than a long list of small doubts.