Answer first
A fake IW371491 is a watch sold as an IWC Portugieser Chronograph that IWC Schaffhausen did not build. The real reference is a stainless steel Portugieser Chronograph with a 40.9 mm case and calibre 79350 inside. Copies of it exist at several grades. The tells sit in the caseback engraving, the dial print, the crystal and the chronograph movement.
The genuine reference at a glance
- Model: IWC Portugieser Chronograph
- Reference: IW371491
- Case: stainless steel, 40.9 mm diameter, about 12.3 mm thick
- Movement: calibre 79350, automatic, Valjoux 7750 base
- Power reserve: 44 hours
- Beat rate: 28,800 vibrations per hour
- Dial layout: two registers. Chronograph minutes at 12, running seconds at 6
- Date window: none
Checks that separate real from fake
Case and caseback
Measure the case. A reading of 42 mm or more points to a replica case. Then read the caseback engraving: reference number, case serial, brand name. Cut edges and even depth mark the original. Copy engraving looks shallow and the lettering drifts. Caseback style changed across production runs, so confirm the correct back for the year of the watch before you call it fake.
Dial and hands
Look at the applied numerals and the subdial rings. Original dials carry thin, crisp print of IWC and SCHAFFHAUSEN, and the subdial rings sit on the numeral axis. Copy dials show thick print, soft numeral edges and subdials set off center. Replica hands run thicker and the steel finish reads flat.
Crystal
The sapphire crystal is domed. On many examples the anti-reflective coating sits on both faces. Copy crystals show more glare and a flat top. Run a finger from the bezel to the glass: a domed sapphire has a smooth step.
Movement and thickness
Calibre 79350 ticks at 28,800 vibrations per hour and winds from a 7750 base. If the back is solid you cannot see the movement, so use thickness and weight. Measure the case. A reading of 14 mm or more points to a different case. Ask the seller for a scale photo of the head and compare it with an example you trust.
Price context
Used IW371491 examples list between about $4,500 and $7,500 USD, based on condition, box and papers. Replica copies sell between about $150 and $500. An offer far under the market range is the first sign of a fake or a watch built from mixed parts.
Before you pay
- Ask for a caseback photo with the reference and serial in frame.
- Ask for the head weight and the case thickness.
- Compare the dial print with a photo from an IWC dealer or a known reference photo.
- Ask about service history and the original strap and clasp.
- Buy from a seller with a return window.
Open points
This guide does not confirm the dial color or strap for every production batch of IW371491. Finishes changed between batches. Check the exact configuration with IWC or an IWC service center before you label a watch fake.