Short Answer
IW371438 is a reference number in the IWC Portugieser Chronograph family. A "fake IW371438" is any watch sold under that reference that IWC did not build. Fakes run from cheap quartz copies with printed dials to high-grade replicas that copy the movement layout. Most of them give themselves away in four places: the subdial layout, the dial printing, the caseback engraving, and the movement.
What the Genuine Reference Uses
The genuine Portugieser Chronograph in this reference family runs the IWC caliber 79350, a modified Valjoux 7750 with a 28,800 vph beat rate and about 44 hours of power reserve. The case is stainless steel at about 40.9 mm, water resistance is rated at 3 bar, and the crystal is sapphire with an anti-reflective coating on both faces. The chronograph uses a vertical bi-compax layout: elapsed minutes at 12 and running seconds at 6. A date window sits at 3.
Before You Inspect
- A 10x loupe
- Bright daylight or a neutral lamp
- A caliper for case diameter and thickness
- A timegrapher, or a timing app as a rough stand-in
- Seller photos of the caseback and movement if you buy at a distance
Inspection Steps
- Confirm the reference number cut into the caseback reads IW371438 and is engraved into the metal, not printed on top of it.
- Compare the subdial positions against the vertical bi-compax layout, since many fakes move them to 3 and 9 or fit a 12-hour register.
- Study the dial text under the loupe for ragged edges on the "International Watch Co" and "Schaffhausen" lines.
- Check the date window position and the date disc font against a known reference photo.
- Run the chronograph start, stop and reset, and listen for a crisp mechanical snap instead of a soft jump.
- Time the watch over 24 hours in several positions and compare the daily rate with the figure the seller claims.
- Weigh the watch in the hand and measure the case, because a plated brass case feels light for its size.
- Open the caseback with a watchmaker and read the movement markings, rotor engraving and finish.
Movement Signals
The movement is the hardest part to fake well. A real caliber 79350 shows signed rotor engraving, striped bridges and polished screw heads, and the rotor swings with a wobble you can feel when you tilt the watch. Quartz fakes tick once per second on the running seconds subdial and have no winding rotor at all. A cheap automatic copy may run, but it will not hold the beat rate or the power reserve of a 7750 base.
Price and Seller Signals
A genuine IW371438 changes hands on the used market in the low four figures and up, depending on condition, box and papers. Offers in the low hundreds, stock photos instead of real ones, and a seller who refuses a caseback photo are all warnings. Ask for the serial number, then check that the digits on the caseback match the digits on any paperwork.
What a First Copy Gets Right and Wrong
Higher-grade copies match the case size and the bi-compax layout, and some even use a real 7750-family movement. They still fall short on engraving depth, dial lacquer, and movement decoration. If you want the look of the reference without the genuine price, ask which movement sits inside, whether the caseback engraving is laser cut or stamped, and what the daily rate is before you pay. Note that counterfeit goods face customs seizure in the US and many other countries, so know the rules before you ship or travel with one.