The short answer
On an IW371438, fakes give themselves away in four places: the dial printing and subdial texture, the movement that drives the hands, the caseback engraving and reference numbers, and the way the crown and pushers feel in your fingers. Bad fakes get the outline right and fail at arm's length. Better replicas fix the outline and still stumble on the date font, the snailing inside the subdials, and the pusher action. So the honest comparison is not fake versus real in one step, it is three tiers: cheap fake, high-tier replica, genuine.
If you only have photos, work the dial and the caseback first. If you can hold the watch, work the pushers and the rotor.
What the reference should be
The Portugieser Chronograph family settles most arguments before you even look at the finishing. Know the baseline and half the fakes disqualify themselves.
Fake IW371438 Compared to Genuine Watches
- Case roughly 40.9mm across, about 12.3mm thick, stainless steel, 30m water resistance.
- Chronograph with a 30-minute counter at 12 and running seconds at 6, date at 3.
- Sapphire crystal, 20mm lugs, sapphire or solid caseback depending on production year.
- Earlier references in this family ran a modified Valjoux 7750 (Calibre 79350). Later ones moved to the in-house 69355 with a longer power reserve.
- 28,800 vibrations per hour, which is eight beats per second. That number matters later.
1. Dial printing and subdials
Genuine printing sits on the dial like it was printed by a machine that costs more than a car. Edges are crisp under a loupe, letters have consistent weight, and the numerals are applied with a clean bevel. Fakes show ink spread, uneven spacing, or a logo that is slightly too heavy on one side.
The subdials are the better test. Genuine subdial rings carry fine concentric snailing and the hands sit at the right height above the recess. Fakes either skip the snailing, print flat rings, or set the hands too high so they cast a hard shadow. Look at the spacing between the subdial edge and the printing above it. It is small on the real thing and often slightly off on a copy.
2. The movement behind the hands
A 7750-based chronograph has a character you can feel. The rotor wobbles when you move your wrist, the chrono pushers have a short firm travel with a distinct click, and the sweeping seconds hand moves in eight small steps per second.
- Quartz fake: chrono seconds hand ticks once per second. Instant fail.
- Cheap mechanical fake: 21,600 vph, so six beats per second, visibly choppier, and the pushers feel mushy.
- Good replica: correct beat rate, but the reset sometimes overshoots or the minute counter lags by a hair.
A timegrapher settles it in ten seconds. Ask for a rate and amplitude reading in the listing photos, or bring a phone app and listen.
3. Case, lugs and finishing
Genuine brushing runs in one direction and stops at a crisp edge. Polished flanks are mirror-clean without waviness. Fakes show slurry brushing that changes direction near the lugs, and polishing that looks slightly soft, like it was done by hand with a buffing wheel.
Flip the watch and look between the lugs. Genuine lug undersides are finished, not left raw. The lug holes sit in the same place on both sides, and the caseband curve is symmetric when you sight down the case.
4. Caseback and reference numbers
Engraving depth is the tell. Genuine engraving is sharp-walled and consistent in depth across the whole circle. Fakes engrave shallow, and the letters look rounded under a loupe. The reference number should appear between the lugs, and the caseback text should match the production era of the watch. Check the serial against the movement number if the caseback is see-through.
5. Crown, pushers and the date
The crown on a genuine pulls out with a firm two-position detent and the date clicks over cleanly at midnight, not at 11:50 or 12:20. Fakes drift. Pushers on a genuine return with a springy snap, not a soft push. Wind it ten turns and listen for a dry, even sound rather than a gritty one.
Date font is a common miss. Genuine numerals are narrow and upright. Replicas often use a wider, bolder font that reads fine at a glance and wrong next to a photo.
6. Strap and buckle
Genuine straps in this family are usually alligator with hand-finished edges and a signed buckle. Fakes use embossed calf, thick edge paint, and a buckle engraving that is deeper than it should be or missing the right mark. The strap is easy to swap, so do not judge the watch by it alone, but a mismatched strap and buckle combo is a hint.
What each price tier gets wrong
- Under $150: wrong beat rate, flat subdials, painted indices, hollow feel.
- $150 to $400: decent silhouette, wrong date font, sloppy caseback engraving, weak pushers.
- $400 and up: close on the wrist, correct beat rate, but the snailing, the printing edges, and the reset behavior still separate it from the real thing.
How to check one before you pay
- Ask for a macro shot of the dial at 12 and at 6. Look at printing edges and subdial texture.
- Ask for a video of the chrono start, stop, and reset. Watch the sweep and the snap back to zero.
- Ask for a timegrapher photo and a caseback shot with the serial legible.
- Ask for the weight of the head. A watch that feels light in the hand usually is.
- Compare the dial layout against IWC's own reference photos for the exact variant, since dial colors and hands changed across the run.
Bottom line
Judge the IW371438 by the movement first, the dial second, and the paperwork last. A sharp dial on a 21,600 vph movement is still a fake, and a slightly soft print on a correct 7750 base is usually a replica worth its price. Know which one you are buying and the comparison stops being confusing.