Short answer

A fake IW371427 is a replica of IWC's Portugieser Chronograph. The genuine watch is a 40.9 mm steel chronograph with the classic two subdial layout, leaf shaped hands, applied numerals and no date window. Copies of this reference run from cheap quartz toys to solid automatic builds, and the difference between them comes down to three things: the movement inside, the dial printing, and how the case was finished. Judge those three and you can size up any copy in a minute.

What the real IW371427 looks like

It sits in the Portugieser Chronograph family, the reference line IWC has built around the same basic recipe for years. The case is stainless steel, roughly 40.9 mm across and a bit over 12 mm thick, with a slim bezel, long lugs and a domed sapphire crystal. The dial is the signature part: a 30 minute counter at 12, running seconds at 6, leaf shaped hands, applied numerals, a rail track minute ring, and no date. Inside sits the 79350, a Valjoux 7750 base that IWC reworked with its own chronograph module and its own finishing. A display back is standard, and that matters once you start comparing copies.

Where a fake usually shows itself

  • Thickness. The subdial layout at 12 and 6 needs extra hardware between the movement and the dial. Cheap builds skip the work, so the case grows. Put a caliper on it, or just look at the profile from the side.
  • Subdial position. On the real watch the two counters sit close to the centre and to each other. On a sloppy copy they drift outward or sit low, and the printing on them goes soft.
  • Dial printing. Look at the numerals under a loupe. Genuine applied markers have crisp edges and sit flat. Copies show rounded corners, uneven lume fill and a logo that is too bold or slightly the wrong shape.
  • Hands. Leaf hands should be polished and faceted, with a clean edge down the middle. Fakes are often flat, roughly cut, or slightly too thick.
  • Caseback. The engraving on the back is a fast tell. Real engraving is sharp and shallow. Copies are usually laser etched deeper and look cloudy.
  • Crown and pushers. Pushers should feel firm with a short travel. Mushy or wobbly pushers point to a cheap movement and a cheap case.

The movement is the tell you can hear

Wind the watch and listen. A 7750 based automatic has a rotor that spins freely and a distinct wobble when you flick your wrist. Quartz copies are silent and the seconds hand ticks. If the running seconds at 6 jumps once a second, the watch is quartz no matter what the dial says. A lot of low grade copies also fake the chronograph entirely: the pushers move a hand or two but nothing actually measures elapsed time.

What to check if you are buying a replica

If you are shopping the replica market rather than trying to catch a counterfeit, the checklist flips a little. Ask what movement is inside before anything else. A 7750 based automatic with a working 12 and 6 layout is the minimum worth paying for. Then run the chronograph. Start it, let it run a minute, stop it, reset it. The hand should snap back to zero without drifting, and the pushers should feel crisp both ways.

Next, look at the parts you actually see. Check the crystal for glare control and for a domed shape rather than a flat disc. Check that the strap or bracelet fits the lugs without a gap. Check that the dial is centred and the markers line up with the minute ring. Small alignment faults are what you notice after a week, not on day one.

Price expectations

Quartz copies sit at the bottom, automatic 7750 builds in the middle, and the better finished pieces at the top. Paying more does not automatically get you a better watch, so spend the money on the movement and the dial rather than on packaging. A clean automatic copy with a sharp dial beats a fancy box every time.

Bottom line

The IW371427 is a simple watch to copy badly and a hard one to copy well. If you are buying, the movement and the dial decide everything. If you are checking whether something is genuine, thickness, subdial placement and the caseback engraving will settle the question faster than any serial number search.