The short answer
A fake IW371652 fails three checks first: the movement, the caseback engraving, and the dial print. A genuine IWC Portugieser Chronograph in the 3716 family runs in-house calibre 69355, a column wheel chronograph with a 46-hour power reserve. Most fakes use a Valjoux 7750 clone or a Chinese chronograph module. Look through the sapphire caseback before you look at anything else.
What the reference should be
The Portugieser Chronograph 3716 has a stainless steel case about 41 mm across and about 13 mm thick. Lug width is 20 mm. Water resistance is 30 m. The crystal and the display back are sapphire. The dial carries two subdials: a 30-minute counter at 12 o'clock and small seconds at 6. The date sits at 3.
IWC assigns 3716-xx numbers to steel, gold, and boutique variants. The IWC catalogue is the source for the dial color, case metal, and strap tied to IW371652. Not every regional catalogue lists every number, so confirm the code with IWC before you treat a listing as genuine.
Movement
Calibre 69355 beats at 28,800 vibrations per hour and holds 46 hours of reserve. The rotor carries IWC branding and a movement number. A 7750 clone shows a different bridge layout and a cam-and-lever chronograph under the rotor. The 69355 has a column wheel at the center of the chronograph works, and it is visible through the back. Watches that claim a 69355 but show a decorated 7750 are the common case.
Caseback and numbers
Genuine engraving is crisp and shallow. Look for the reference number, the case number, and the IWC name. Fake engraving runs deep, rounds at the edges, or shows a fuzzy laser border. Serial numbers on fakes repeat across listings. Search the number before you pay. If it appears twice, the watch is a copy.
Dial and hands
Print on a genuine dial is thin and flush. The three letters of the IWC mark are spaced wide. Fakes thicken the strokes and crowd the spacing. The subdials sit on one vertical line through the center. On fakes the subdials shift a fraction of a millimeter and the date window sits off-center. Applied indices on the 3716 are polished on top and matte on the sides. Fakes plate the whole index in one finish.
Chronograph hands on the genuine watch reset to zero and stop. A 7750 clone can drift a second or more after a reset.
Size, weight, and strap
Weight is a weak test. Steel is steel, and a heavy fake is easy to build. Measure the case with calipers instead. Ask the seller for a diameter reading and a height reading. Copies differ from the reference figure by 1 mm or more. Strap stitching on fakes runs uneven at the buckle end, and the leather is stiff at room temperature.
Price and paperwork
The steel Portugieser Chronograph lists in the mid four figures in US dollars. Secondhand prices sit below retail. A "new" IW371652 at a few hundred dollars is a replica. That is the whole test. Boxes and papers get copied, so treat them as support, not proof. The warranty card number should match the caseback number.
Replica market notes
Replica IW371652 watches sell from about $150 to $600 by tier. Sellers use "Swiss made" and "1:1" as labels, not as standards. No replica carries a genuine 69355. US Customs and Border Protection can seize counterfeit watches at import, and that risk sits with the shipment.
Checklist
- Open the caseback. Look for a column wheel and the 69355 layout.
- Compare the subdial line to the hand stack. Any offset is a fail.
- Read the engraving under magnification. Fuzzy edges are a fail.
- Ask for caliper readings on diameter and height.
- Match the warranty card number to the caseback number.
- Compare the asking price to current listings. A large gap points to a replica.