Short answer
A replica IW371651 copies an IWC Portugieser Chronograph from the 3716 reference block. The real watch has a 41 mm steel case about 13.1 mm thick, two dial registers, chronograph minutes at 12, running seconds at 6, a date at 3, and IWC caliber 69355 under a sapphire case back. Copies are judged on those measurements and on how the chronograph behaves, not on how the watch looks in a listing photo. Thickness, dial print, and pusher feel are where most fakes give themselves away.
Genuine reference points
The Portugieser Chronograph carries two registers, one at 12 and one at 6, with a date window at 3 o'clock. The case measures about 41 mm across and about 13.1 mm thick, and water resistance is rated at 3 bar. The current movement is IWC caliber 69355, a column wheel chronograph with a 46 hour power reserve and a rate of 28,800 vibrations per hour. Earlier 3714 versions of the same line ran a Valjoux 7750 base, so a seller who claims a Swiss movement without naming the caliber is telling you nothing.
Prerequisites
- A published spec sheet for the reference, listing diameter, thickness, lug width, and water resistance
- Digital calipers
- A 10x loupe
- Clear photos of a known real example, including the case back and the dial shot at an angle
Inspection steps
- Lay the watch flat and measure the case across the bezel at the 2 and 8 o'clock line with the calipers.
- Measure total thickness from the case back to the highest point of the crystal.
- Compare both numbers with the published figures and note any gap larger than 0.3 mm.
- Start the chronograph and run it for 30 minutes against a phone timer to confirm the counter at 12 advances once per minute.
- Stop the chronograph, reset it, and check that the minute hand snaps back to zero without drift.
- Set the date through a full month and watch the numerals for centering and font weight.
- Inspect the dial print with the loupe, checking letter spacing in the brand name and the shape of the applied numerals.
- Turn the watch over and read the case back engraving, then compare rotor finishing against photos of a real example.
- Press each pusher and rank the resistance by feel, since a soft pusher points to a low grade movement.
- Time the watch over 24 hours against a reference clock and record the daily rate.
Common tells on a copy
- Case thickness above 14 mm on a watch sold as a 13 mm reference
- Subdial hands sitting at the wrong height so they cast a shadow on the dial
- A date window cut without a beveled frame
- Printed dial text that reads flat and slightly fuzzy under magnification
- A crown that spins without engaging the stem, or pushers that wobble
- A ticking seconds hand, which means a meca-quartz module rather than a mechanical chronograph
Legal and ownership reality
Counterfeit watches infringe registered trademarks, and in the United States the sale and import of them can lead to customs seizure, civil damages, and criminal charges. A copy also carries no warranty, no service support from IWC, and almost no resale value. Repair on a copied chronograph often costs more than the watch itself, because independent watchmakers may decline to work on unbranded or mismatched movements.