Short answer

IW371646 is an IWC reference number in the Portugieser Chronograph line. A fake IW371646 is a watch built by another factory that carries IWC markings. No single photo proves a watch is real. Four checks cover most cases: subdial layout, movement beat rate, caseback engraving, and date wheel font.

What the reference covers

IWC uses the IW3716xx block for the Portugieser Chronograph. The case measures 41 mm across and about 13 mm thick. Sapphire covers the dial and the caseback. The strap is alligator leather on a steel pin buckle or folding clasp. Water resistance is 3 bar.

The watch runs an in-house 69000-series chronograph calibre. Dial colors, strap options and edition markings change between variants. Check the exact variant on IWC's site before you compare a watch against it. Public listings do not state which dial color belongs to IW371646, so confirm that first.

Subdial layout

The dial has two subdials. The counter at 12 records chronograph minutes. The counter at 6 runs the seconds. A date window sits at 3. Many counterfeit movements are modular chronographs from third-party suppliers. Those movements push running seconds to the 9 position or move the date to 4:30. A watch with that layout is not an IW371646.

Movement

Genuine 69000-series calibres beat at 28,800 vibrations per hour, or 4 Hz. A timegrapher reading of 21,600 vph points to a different movement. Look at the rotor. IWC engraves the calibre number and the IWC name. Fakes use shallow laser etching or omit the calibre number. Screw heads on a real movement sit flush and show polished slots.

Case and caseback

Engraving on a genuine caseback cuts into the metal. Replica engraving sits on the surface and reads faint under a loupe. Check the reference number, the serial number, and the International Watch Co. line. Font weight and letter spacing matter more than the words. Crown threads should engage in under two turns with no grit.

Dial, hands and date

Applied numerals on a genuine dial have polished bevels. Printed text stays sharp at 10x magnification. The date wheel font on a replica runs wider or bolder than the font IWC uses. Hand length reaches the minute track. Replica hands stop short of it or run past it.

Weight and finish

A steel Portugieser Chronograph with a leather strap weighs roughly 80 to 90 g. Replicas land outside that range by 10 g or more. Case edges on a real watch are crisp. Polished and brushed surfaces meet on a hard line. Replicas show a soft, rounded transition.

Price reality

A genuine Portugieser Chronograph sells in the four-figure range on the secondary market. Counterfeits sell from under $100 to a few hundred dollars. A seller who offers a new IWC at a fraction of retail price is offering a copy.