The short answer
The IW371438 is a steel Portugieser Chronograph from IWC: a 40.9 mm case, a two-register dial with running seconds at 6 and a 30-minute counter at 12, and calibre 79350 inside, which is a heavily reworked Valjoux 7750. The caseback is solid, so nobody sees the movement. That matters, because it means a fake has to win or lose on the outside. Most copies get the silhouette close and then give themselves away at the subdial hands, the crystal, and the engraving on the back.
What the genuine reference is
Before you judge anything, know the shape you are comparing against.
- Steel case of about 40.9 mm, with a narrow bezel and long lugs
- Two registers only, no date, no third subdial
- Applied numerals and markers, gold or rhodium plated depending on the dial variant
- Leaf-shaped hour and minute hands, thin chronograph needle
- Sapphire crystal with anti-reflective coating on both faces
- Alligator strap on an IWC-signed pin buckle
- Solid steel caseback stamped with reference and case numbers
Where the copies slip
Subdials and hand lengths
This is the tell I check first. On the real dial the small hands stop short of the printed track by a consistent margin, and the two registers sit on a clean vertical axis. Cheap copies fit hands that are too long, too thick, or blunt at the tip. Subdial surfaces on the genuine watch are snailed and catch light in rings; flat or matte printing is a red flag.
Crystal
IWC coats sapphire on both sides, which is why a genuine dial looks like it has no glass over it. Many replicas use a single coating or none at all, so you get a purple or blue tint at an angle, or a visible reflection where the real thing would be clear. Cup your hand over the dial in daylight and look at the crystal from the side.
Caseback engraving
Run a light across the back at a low angle. Genuine engraving is crisp, deep, and evenly spaced. Fakes are usually laser-etched and shallow, so the lettering washes out the moment light stops hitting it straight on. Check the spacing of the reference number and how the case number sits under it.
Chronograph feel
Push the top pusher and listen. A real 7750-based chronograph starts with a firm, short click and the needle snaps from zero without a stutter. Reset and watch where the needle lands: it should return exactly to 12. Copies often creep a hair past the mark or hesitate before moving. Mushy pushers with a long travel are common on the lower tiers.
Why not to obsess over the movement
Here is the awkward part. Because IWC builds the 79350 on the Valjoux 7750 platform, plenty of replicas run a 7750 or a close copy of it, and the underlying architecture is not wildly different. That is why you cannot settle this debate with a spec sheet. What separates them is finishing, regulation, and how the thing behaves in your hand over a full day: does it gain or lose time, does it wind smoothly, does the rotor spin with a rattle. Since the back is closed, judge it by behavior, not by photographs of a decorated rotor you will never see.
Strap and buckle
Straps are the cheapest thing to swap, so do not read too much into one. That said, genuine alligator has a tight scale pattern that bends with the strap, and the stitching is fine and even. Replica straps are often embossed leather with wide, waxy thread. The buckle should be stamped, not cast, with sharp edges and plating that matches the case finish.
A five-minute check before you buy
- Open a factory photo of the exact dial variant and compare subdial hand lengths and positions.
- Look at the crystal from three angles for tint or haze.
- Rake a light across the caseback and read every character.
- Start, stop, and reset the chronograph four or five times.
- Wind it slowly and feel for grit or slip in the crown.
- Flex the strap and check the buckle stamping.
Price is its own tell
A real steel Portugieser Chronograph changes hands in the thousands, and condition, box, and papers move that number a lot. If an asking price looks like a rounding error next to the secondhand market, you already have your answer. The same goes for a seller who cannot show a service history, a receipt, or a clear photo of the caseback numbers. No amount of good lighting fixes paperwork that does not exist.