Short answer
A fake IW371498 is a copy of the IWC Portugieser Chronograph, a 40.9mm steel watch with a closed caseback, two subdials and IWC's calibre 79350. Replica builders lean on this reference because the real movement is a modified Valjoux 7750, and the Asian 7750 clone already exists in huge volume. That makes a passable copy cheap to produce. It also means the tells are mostly mechanical rather than cosmetic, so knowing where to look matters more than knowing what to photograph.
What the genuine reference actually is
Keep the numbers in your head: 40.9mm across, around 12.3mm thick, 20mm lugs, sapphire crystal, solid caseback. The steel versions carry a silver plated dial with applied numerals that sit proud of the surface and catch light along their edges. The subdial at 12 runs the 30 minute counter. The one at 6 runs the small seconds. There is no date window at 3, and that single fact trips up more replicas than anything else on the watch.
The strap is alligator on a steel pin buckle or deployant, tapering from 20mm at the lugs to 18mm at the clasp. Water resistance is rated at 3 bar, which is polite language for splash resistant.
The movement is where fakes show themselves
IWC took the 7750, deleted the date function, and finished it to a standard the 7750 never saw in a workshop in the Jura. Replica builders take an Asian 7750 and either leave a date wheel sitting under the dial or fit a hidden date that creeps when you set the hands. Two checks catch nearly all of them.
First, pull the crown to the first position and turn. If the hands move and something drags behind them, there is a date mechanism in there that should not exist. Second, run the chronograph. A genuine 79350 beats at 28,800 vph and starts without a stutter. Cheap copies hesitate on start and snap back a fraction off zero on reset.
Power reserve is worth asking about too. The real calibre runs about 44 hours. Plenty of replicas fade somewhere between 30 and 36, and a seller who cannot answer the question usually knows why.
Case and dial tells
- Thickness. Most replicas land between 13.5mm and 14.5mm because the movement and caseback stack differently. It sounds small. On a 40.9mm dress chronograph it changes how the watch sits under a cuff.
- Caseback. The 3714 family uses a solid back with engraving. A display back is a flag, no matter how nice the movement looks through it.
- Numerals. Genuine dials use applied metal numerals. Printed ones look flat in raking light and lose the shadow line along the edge.
- Subdial spacing and hands. Thin, poorly finished subdial hands are common. On the real thing they are short, crisp and sit close to the dial.
- Crown. Check the fluting and the signature. Soft fluting and a shallow engraving show up fast at arm's length.
- Engraving depth. Genuine caseback text is cut cleanly. Copies often look laser etched, with a grey wash instead of a cut edge.
What price tiers actually buy
Entry level copies get the silhouette right and little else. The dial printing is heavy, the crystal has no meaningful anti reflective coating, and the chronograph works but feels loose. Mid tier is where the reference becomes wearable daily: better case finishing, a closer dial, and a 7750 that has been serviced before shipping. Top tier adds correct thickness, a properly finished dial, and a movement that will hold a rate. The gap between mid and top is smaller than the gap between entry and mid, which is not what most buyers expect.
Checklist before you commit
- Ask the seller for the measured thickness with calipers, not the spec sheet.
- Ask for a photo of the caseback and a photo of the crown from the side.
- Ask which movement is inside, and whether a date wheel is present.
- Ask for a timing reading on a timegrapher, or at least a video of the chronograph starting and resetting.
- Confirm strap material and buckle type, since both are commonly swapped to hit a price.
One last thing worth saying plainly. A replica is not a genuine watch, cannot be serviced by IWC, and cannot be sold as real. Buy it knowing that, and the checks above will get you a better example for the same money.