Short answer

A fake IW371438 fails on four checkable points: dial layout, caseback engraving, movement finish, and case and hand finishing. A genuine IWC Portugieser Chronograph reference 371438 has a 30-minute chronograph counter at 12 o'clock, running seconds at 6 o'clock, no date window, and a Valjoux-based caliber visible through a sapphire display back. Most copies add a date, print the subdial rings instead of cutting them, and stamp the caseback text with shallow, uneven letters.

What the genuine reference is

  • Stainless steel case, roughly 40.9 mm across and about 12.3 mm thick
  • Silver-plated dial with applied gold numerals and feuille hands
  • Two subdials: chronograph minutes at 12, small seconds at 6
  • No date window, no day window, no 24-hour indicator
  • Caliber 79350, a Valjoux 7750 base modified by IWC
  • Sapphire crystal front and back, water resistance rated at 3 bar
  • Black alligator strap with a steel pin buckle

Check the dial and hands

  1. Look at the 3 o'clock position. A real 371438 has nothing there. If you see a date aperture, the watch is not a 371438 dial.
  2. Compare the two subdials. Both should sit on the same horizontal axis, level with each other. Copies often mount the 12 o'clock subdial a fraction high.
  3. Run a finger over the subdial rings. Genuine rings are recessed into the dial plate with a crisp step. Fakes use a printed circle that feels flat.
  4. Study the numerals. Real applied numerals cast a hard shadow and have sharp, polished edges. Stamped copies look soft and slightly rounded.
  5. Check the hands against the minute track. Feuille hands on the original taper to a fine point that reaches the printed track. Copy hands are usually blunt or too short.
  6. Angle the dial toward a light. Genuine silver plating shifts tone evenly. Fake dials show patchy, milky reflections or a visible print texture.

Check the case and caseback

  1. Read the engraving on the back. Letters should be deep, even, and filled with a consistent finish. Shallow or wobbly text is the single most common giveaway.
  2. Confirm the reference number matches the case metal and dial color. A 371438 is steel with a silver dial. Mixed combinations point to a swapped or fake caseback.
  3. Examine the lugs from underneath. Genuine lugs are polished on top and satin-finished on the sides with a clean transition line.
  4. Check the crown and pushers. Pushers should screw down or seat with a firm, short travel. Mushy or long-travel pushers suggest a generic case.
  5. Weigh the watch. A steel 371438 feels dense and cold in the hand. Many copies use lighter alloys or thin case walls.

Check the movement

  1. Hold the watch to light through the display back. You should see a rotor, bridges with Geneva stripes, and perlage on the base plate.
  2. Look for the IWC signature on the rotor. Copies either omit it or engrave it with a laser that leaves a brown burn edge.
  3. Start the chronograph and watch the 12 o'clock hand. It should snap to zero and sweep smoothly. A stuttering reset points to a cheap module.
  4. Listen to the rotor. A genuine 7750 base winds with a soft metallic whir. A loud grinding or rattling noise is a warning sign.

Check the strap, buckle and paperwork

  1. Inspect the buckle engraving. It should match the caseback font exactly.
  2. Check the leather. Original alligator has a fine, irregular scale pattern. Embossed cowhide shows repeating, uniform scales.
  3. Compare box printing to the warranty card. Serial numbers must match across card, caseback and paperwork.
  4. Ask for a service record. IWC service papers list the movement number and can be verified with the factory.

Where copies still fall short

Well-made replicas can pass a photo check. They rarely pass a loupe check. The dial print on a copy thickens under magnification, the applied numerals sit on pads that are too tall, and the caseback threads feel rough when you unscrew the back. Movement decoration is the hardest part to fake at low cost, so the rotor and bridges are where most copies give themselves away.

When to get a professional opinion

If two or more checks fail, stop negotiating and take the watch to an authorized IWC service center or a watchmaker with IWC parts access. A movement service quote is cheap compared to the cost of a counterfeit. Ask the seller for a written return right before any money changes hands, and pay in a way that can be reversed.