Quick answer
A fake IW371650 shows up in four places: the movement, the counter at 12 o'clock, the case finishing, and the caseback text. Genuine watches run IWC calibre 89361. Copies run a Valjoux 7750 or a Seagull ST19 behind a decorated plate. Check the serial with IWC or an authorized dealer before you pay.
What IW371650 is
IW371650 sits in the Portugieser Chronograph Classic group, reference family IW3716. The case is stainless steel, 42 mm across. The movement is the in-house automatic calibre 89361, with a 68-hour power reserve and a 4 Hz balance. Two subdials: small seconds at 6 o'clock and a combined hour and minute counter at 12 o'clock. Date at 3 o'clock. Sapphire crystal front and back. IWC uses the last three digits of a reference for one case, dial and strap combination, so confirm the dial color and strap for the 650 suffix against the IWC catalog. If a seller describes a different case size or a different date position, that description is wrong.
Movement
Look through the display back.
- Genuine: Geneva stripes on the bridges, blued screws, perlage on the main plate, and the calibre number 89361 stamped on a bridge.
- Genuine: 68-hour power reserve. Wind it, set it down, and check after two days.
- Copy: a 7750 base runs about 42 to 48 hours and beats at 28,800 vph with a different bridge shape.
- Copy: a hand-wound ST19 has no rotor.
Counter at 12 o'clock
Start the chronograph and watch the top register. Calibre 89361 puts two hands on that one dial: one counts minutes, one counts hours. A fake with a 30-minute counter stops at 30. A fake with a 12-hour counter uses one hand, not two.
Case and crown
Genuine cases have a sharp line where the polished flank meets the brushed side. Lugs are crisp. The crown sits flush against the case tube. Fakes show rounded edges, a wide gap between lug and strap, and a crown that stands proud. Check the bezel from the side: genuine is flat with a small chamfer, and the reflection breaks in a straight line.
Dial
Genuine dials use applied numerals and indices with sharp edges. Printing is thin and even. The IWC logo and the Schaffhausen line sit level with the 12 o'clock position. On fakes the type is heavier, the spacing shifts, and the numerals sit at unequal heights. Lume on the hands and indices matches in color under low light.
Caseback and serial
The caseback is engraved with the reference number and a case serial. Ask for both in a photo before payment. Fakes often share one serial across many units. IWC and authorized dealers can check a serial against their records. A service invoice with the same serial is stronger evidence than any photo.
Price and paperwork
Used IW371650 examples sell for about $6,000 to $9,000 with box and papers. Prices move with condition and the market, so compare sold listings, not asking prices. A "new" example at $1,200 is not a genuine watch. Genuine sets include the box, a warranty card with a retailer stamp and date, and the instruction booklet. Missing papers lower the price. They do not explain a price that low.
What a visual check cannot do
A photo check does not prove a watch is genuine. Case clones with genuine dials exist. So do genuine cases with swapped movements. Service records, an IWC extract from the archives, or an inspection by a watchmaker with the right tools settle the question. If a seller refuses a serial check or a third-party inspection, stop.