Short answer
A fake IW371649 is a watch that copies the look of the IWC Portugieser Chronograph. The true reference uses a 41 mm steel case and IWC caliber 69355. Four checks settle most cases: the subdial layout, the crystal, the movement, and the caseback engraving.
What the reference number covers
IWC groups the current Portugieser Chronograph under the 3716xx block. The case measures 41 mm across and about 13 mm thick. Water resistance is 3 bar. The dial carries two counters: a 30-minute chronograph totalizer at 12 o'clock and running seconds at 6 o'clock. There is no date window. The crystal is sapphire with coating on both faces, and the caseback has a sapphire window.
On the exact number: public sources do not publish a full dial and strap breakdown for IW371649. Confirm dial color, strap, and production year with IWC before you compare a watch against that number.
Check 1: Dial layout
- Genuine: 30-minute counter at 12, small seconds at 6, no date.
- Fake: counters at 3 and 9, a date at 3, or a 12-hour counter at 6.
The two counters sit on the 12-6 axis. Numerals are applied metal, not printed ink. Raised numerals catch light on their edges. Printed numerals look flat under the same light.
Check 2: Case and crystal
Measure the case with calipers. Copies often measure 40 mm or 42 mm. Test the glass with the edge of a steel blade on a hidden spot near the case flank. Mineral glass scratches. Sapphire does not. A strong blue tint under a lamp points to mineral glass with a coating.
Check 3: Movement
Caliber 69355 runs at 4 Hz, or 28,800 vibrations per hour, with a 46-hour power reserve. Start the chronograph and watch the sweep. A 4 Hz hand moves in 8 steps per second. A quartz fake ticks 1 time per second. A 3 Hz copy steps 6 times per second. Count the steps against a phone timer.
Look at the rotor through the display back. Text on the rotor and bridges should be crisp and recessed. Ask for a movement photo before payment. No copy carries caliber 69355. IWC builds that movement for its own watches.
Check 4: Caseback and serial
IWC stamps the reference number and an 8-digit serial on the caseback. Check the font: even depth, sharp edges, no tool marks around the letters. Cross-check the serial with IWC service. A serial that contains letters, or laser etching with a grey haze, points to a copy.
Copy grades
- Low grade: quartz or basic automatic movement, mineral glass, printed dial text, case size off by 1 mm or more.
- Mid grade: automatic chronograph movement such as a Valjoux 7750 or a clone, sapphire glass, dial layout close but not correct.
- High grade: automatic chronograph, sapphire glass, 41 mm case, applied numerals, caseback engraving close to the original.
Papers, box, and price
Genuine watches ship with a warranty card, a booklet, and a box that carries the reference. Sellers of fakes reuse genuine boxes and papers. Match the serial on the card to the serial on the caseback. If the two numbers differ, stop.
A price far below the market for the reference is a warning sign. Check completed sales for the same reference and year before you pay.
What to do next
Ask the seller for four photos: dial face, caseback, movement, and side profile. Shoot your own watch with the same four angles to compare. When in doubt, take the watch to an IWC boutique or a watchmaker with a timing machine. A timegrapher prints beat rate and amplitude. A reading of 28,800 vph matches caliber 69355.