The IW371628 sits in the IWC Portugieser Chronograph family, so most counterfeits fail on movement architecture, dial printing, and case finishing rather than on one obvious flaw. Authenticate in this order: case measurements, dial and hands, movement through the display back, then serial numbers and paperwork. A visual pass is not proof of anything. Only IWC Schaffhausen or a qualified watchmaker can confirm the watch once the case is opened.

Reference Points to Verify First

The 3716-generation Portugieser Chronograph measures 41mm across the case, about 13mm thick, with 20mm lugs. The dial carries a bi-compax layout with subdials at 12 and 6, applied numerals, leaf-shaped hands, and a printed minute track. The movement is the in-house calibre 69355, an automatic column-wheel chronograph running at 28,800 vph with roughly 46 hours of power reserve. A sapphire display back shows the movement. Confirm those specs against the exact reference before you judge anything else.

Step-by-Step Authentication

  1. Measure the case with digital calipers and compare diameter, thickness, and lug width to the published figures.
  2. Examine the dial printing under 10x magnification and check letter spacing, numeral thickness, and the crispness of the minute track.
  3. Check the subdial positions and hand lengths, since copies often place the 12 and 6 registers a fraction off center.
  4. Inspect the date window for a clean cutout and a date font that matches IWC's own.
  5. Run a fingernail along the case flanks and bezel edge to feel for sharp transitions or polishing that bleeds onto brushed surfaces.
  6. Press the pushers and confirm a firm start, a crisp stop, and an instant flyback to zero with no drift.
  7. Turn the crown and feel for smooth winding with no grit, then check the engraved IWC logo on the crown.
  8. Read the caseback engraving and compare the font weight and depth to reference photos.
  9. View the movement through the display back and confirm the column wheel, balance bridge shape, and rotor engraving.
  10. Match the caseback serial, the movement serial, and the warranty card digits against each other.
  11. Take the watch to an authorized dealer or IWC service center for a database check.

Movement Red Flags

  • A closed steel caseback on a reference that should have a sapphire display back.
  • A rotor with printed text instead of engraved text, or a generic 7750-style chronograph module.
  • Rough perlage, uneven Geneva stripes, or burrs on bridge screws.
  • A balance wheel that runs at 21,600 vph instead of 28,800 vph.
  • Chronograph seconds that stutter or fail to reset to the exact 12 o'clock position.

Papers, Box, and Serial Numbers

Genuine IW371628 examples ship with a warranty card, a matching box, and a manual with the correct reference printed on it. Ask for the original purchase invoice when the seller claims a recent sale. Cross-check the serial on the caseback against the card. Serial numbers on IWC watches are engraved, not laser-etched, and sit straight within the caseback ring.

Limits of a Visual Check

Well-built replicas now copy dial proportions and case geometry closely, so a photo review or a hand inspection in a parking lot proves little. A watchmaker with a timing machine and a caseback opener can settle the question in minutes. If the seller refuses an inspection, treat that as the answer.