The short answer
A fake IW371752 is a replica of IWC's Portugieser Chronograph, and the number matters less than people assume. Inside the IW3717 family, the trailing digits mostly identify a dial, hand and strap combination. Case, layout and movement architecture stay close to identical across the range. That helps a replica buyer, because the checks do not change with the suffix. Look at the subdials, the crystal, the case thickness and the pushers, and you will know in about a minute whether you are holding a serious copy or a toy.
What the original does, and why copies struggle
The Portugieser Chronograph is a clean two-register watch. Running seconds sit in the lower subdial, the chronograph minutes counter sits up top, and the dial carries leaf hands, applied numerals and a thin polished bezel. The case measures a hair under 41 mm across and roughly 12 mm thick. None of that sounds hard to copy. In practice the proportions are unforgiving. A fraction of a millimetre on the bezel or a slightly wrong lug curve changes how the watch sits on the wrist and how the dial reads. Copies built to a low price end up chunkier, with a flat dial and a bezel that crowds the dial opening.
The earlier generation used calibre 79350, an ETA/Valjoux 7750 base, and the newer generation switched to the in-house 69355. Both are automatic chronographs, which is why the case has height and the pushers have a mechanical snap. Copy makers fight the same physics, and it shows in the measurements.
Where replicas give themselves away
Dial and subdials
Printing is the first filter. Genuine text sits crisp under magnification, with even stroke weight. Cheap copies look slightly fuzzy or thick. The subdial rings on the original have a fine concentric texture, and the counters are recessed. Flat, painted subdials are a bad sign. Applied numerals should be sharp-edged and properly polished, not soft blobs with rounded corners. Then watch the lower subdial for ten seconds. A mechanical movement produces a smooth, high-frequency sweep. A quartz copy ticks once per second, and no amount of good casework hides that.
Case, crystal and thickness
Ask the seller for a caliper photo. Anything past about 13.5 mm thick is usually a stacked clone movement in a case built to hide it. The sapphire crystal on the original has anti-reflective coating on both faces, which gives the dial a faint blue or purple cast at an angle. Mineral glass looks duller and scratches faster. Run a fingernail along the caseband and lug edges. Real cases are polished and brushed in separate zones, with a visible break line. Copies often blur the transition.
Movement and pushers
Start the chronograph, let it run a minute, then reset. A 7750-based movement resets with a firm, single snap and the hand lands at twelve. A cheap clone hesitates or overshoots. The top pusher should feel like a short, positive click, not a sponge. Automatic 7750 copies also wobble slightly on the wrist and make a faint rotor whir. That sound is normal. Silence plus a ticking seconds hand means quartz.
Caseback, strap and clasp
Engraving on the back should be deep and even, with legible reference stamping. Rotor decoration on better copies is decent and on cheap ones is a printed sticker. On the strap, check stitch density and edge finishing, and confirm whether the clasp is a folding deployant or a plain pin buckle. Sellers who cannot answer that question usually have not handled the watch.
Rough price bands
- Under about $120: quartz or a low-grade automatic, mineral glass, flat subdials. Fine as a novelty, not as a watch.
- Around $150 to $350: Asian 7750 clone, sapphire crystal, acceptable dial printing, correct subdial placement.
- Around $350 to $700: decorated movement, double AR coating, closer case dimensions, better strap hardware. This is where the differences start to matter.
What to ask before you pay
- Which movement is inside, and does the lower subdial sweep or tick?
- What are the measured case diameter and thickness?
- Sapphire or mineral crystal, and is the coating on one side or both?
- Do the pushers screw down, and what is the water resistance rating?
- What is the return policy if the watch arrives with a misaligned hand or a dead chronograph?
- Are the photos of the actual unit or a stock image?
Five-minute checklist
- Sweep test on the running seconds subdial.
- Chrono start, stop and reset, twice.
- Subdial position at exactly 12 and 6, not drifting.
- Crystal clarity and coating tint at an angle.
- Case thickness against the stated figure.
- Sharp dial printing under a phone macro lens.
- Pusher feel and crown threading.
One last warning. Replica sellers advertise replicas. Sites listing a fake IW371752 as a genuine IWC at two thousand dollars are running a different game, and the watch that arrives will not match the photos. Buy the seller as much as the watch, and keep the reference number in perspective. It is a label on a dial, not a promise about what is inside the case.