Short answer
IW371618 is a reference number in the IWC Portugieser Chronograph family. Watches sold under that number for a few hundred dollars are counterfeits. IWC lists this model in the high four figures in US dollars. Confirm the exact dial color and case metal for IW371618 in the IWC catalog before you compare a watch to online photos.
What the reference is
The Portugieser Chronograph uses a two-register dial: a 30-minute counter at 12 o'clock and running seconds at 6 o'clock. The case measures about 41 mm across. Steel, gold, and two-tone versions sit inside the IW3716 family. IW371618 is one variant of that family. IWC's reference page is the source for its dial, hands, and strap.
Movement: the first tell
Portugieser Chronograph watches built from 2020 onward use caliber 69355, an in-house automatic with a 46-hour power reserve. Those watches have a sapphire display back. Earlier versions used caliber 79350, based on the Valjoux 7750, and had a solid caseback.
- Fakes often show a solid back on a reference that should have a display back.
- Rotor engraving on a genuine movement is deep and crisp. Fake engraving is shallow, printed, or off-center.
- A 7750-based fake cannot produce the 12-6 subdial layout without a module. Check the spacing.
- The balance wheel on a real 69355 sits under a signed bridge. Many fakes leave it open.
Case, dial, and crystal checks
- Case thickness. A real Portugieser Chronograph is about 13 mm thick. Many fakes run 1 to 2 mm thicker.
- Crystal. Genuine sapphire carries an anti-reflective coating with a faint blue tint. Fake crystals show heavy glare.
- Applied numerals and indices. Real ones sit flush and catch light on their edges. Fakes sit high or look painted.
- Subdial rings. The snailed finish on a real dial is fine and even. Fake rings look flat.
- Crown and pushers. Crown engraving is sharp. Pushers on a real watch click with short travel.
- Strap and clasp. IWC used Santoni alligator straps. The clasp is signed.
Serial numbers, papers, and price
IWC engraves a serial number on the caseback and matches it to the reference on the warranty card. Counterfeit sets reuse the same serial number across many watches. A search of that number finds dozens of listings. Registration through IWC's owner portal is a stronger check than a paper card alone.
Price is the fast filter. New Portugieser Chronograph watches sell in the high four figures at US dealers. Used examples hold much of that value. An offer at 5 percent of list price is a counterfeit, not a bargain.
Legal and service notes
US Customs and Border Protection treats counterfeit watches as prohibited merchandise. Shipments face seizure and destruction. IWC service centers refuse counterfeit watches, so a buyer holds a watch that no watchmaker will repair with factory parts.