The fastest way to identify a counterfeit IWC Portugieser Chronograph Classic 42mm is to test the chronograph against the subdial layout. Genuine references in this line, such as IW390302, run IWC calibre 89361. That movement drives a combined hour and minute counter in the subdial at 12 o'clock, running seconds at 6 o'clock, a date window at 3, and a flyback reset. Most fakes copy the dial picture but hide a generic or modular chronograph movement that carries a 30 minute counter at 12 and no flyback. If the subdial at 12 stops or wraps after 30 minutes, the watch is not genuine. The steps below confirm it.

What you need

  • A 10x jeweler's loupe
  • A caliper or a steel ruler
  • Bright, directional light
  • A reference photo of the exact reference number you are checking
  • Time to run the chronograph for 35 minutes

Test the chronograph first

  1. Start the chronograph and note the time.
  2. Let it run for 35 minutes.
  3. Look at the subdial at 12 o'clock. A genuine watch keeps counting hours and minutes there. A fake with a 30 minute totalizer will stop, wrap, or reset itself.
  4. Press the lower pusher while the chronograph is still running. A genuine flyback resets the hand to zero and restarts the count in one press. Most fakes stop or need two presses.
  5. Watch the small seconds at 6 o'clock. It should run without jumping.

Check the dial

  1. Read the IWC and Schaffhausen text with the loupe. Genuine printing has sharp, even strokes and no ink bleed.
  2. Examine the rings inside both subdials. They should carry a fine texture with crisp edges where they meet the dial.
  3. Inspect the date window. The cut should be clean and squared, with the numeral centered and even margins on all sides.
  4. Check the hands. The leaf shaped hands should be polished on the bevels and reach their markers without overshooting.
  5. Tilt the dial into the light. Genuine applied markers sit above the surface and cast a small shadow.

Inspect the case and case back

  1. Measure across the case, excluding the crown. The reading should sit close to 42 mm.
  2. Run a finger along the lugs. They should curve with no sharp tooling marks and no flat, stamped feel.
  3. Turn the watch over and read the engraving. Reference and serial numbers on a genuine case back sit deep, even, and centered.
  4. Look at the crystal from an angle. A genuine sapphire crystal carries anti reflective coating and shows little glare.

Look at the movement

  1. Hold the watch under light and study the finishing. A genuine calibre shows Geneva stripes, polished bevels, and evenly blued screws.
  2. Read the engraving on the rotor. The text should be sharp and correctly spaced.
  3. Look for a plastic movement spacer, which points to a generic movement rather than an in house calibre.

Verify the paperwork and the seller

  1. Write down the reference number from the case back and the serial number.
  2. Compare that reference against the dial layout, case size, and functions you observed.
  3. Ask for the guarantee card, booklet, and box, then check that all numbers match the watch.
  4. Compare the asking price with current market listings for the same reference.

Bottom line

A counterfeit IWC Portugieser Chronograph Classic 42mm fails on function before it fails on looks. Run the chronograph past 30 minutes and test the flyback. If the subdial at 12 is a 30 minute counter, the watch is a fake no matter how good the dial appears. Then confirm the printing, the case back engraving, and the movement finishing. Buy from a seller who puts the reference and serial in writing and accepts a return.