Quick answer
A fake IW371620 gives itself away at the back of the watch, on the dial furniture, and in the feel of the chronograph pushers. The genuine reference is a 41 mm stainless steel Portugieser Chronograph with IWC's in-house calibre 69355, a column wheel, a display back, and roughly 46 hours of power reserve. Replica makers copy the dial layout, the logo, and the box. They rarely copy the movement architecture, the hand finish, or the pusher action. Check those three areas in order and most fakes fall apart in under two minutes.
What the real IW371620 looks like
Confirm the current spec sheet from the maker before you inspect a watch, since IWC has shipped several dial and hand variants across this reference family. The baseline to work from:
- 41 mm stainless steel case, about 13 mm thick
- In-house automatic calibre 69355 with a column wheel chronograph
- Two subdials: a 30-minute counter at 12 and running seconds at 6
- Leaf-shaped hands and applied numerals
- Sapphire crystal on the front and a sapphire display back
- Water resistance rated to 60 m
What you need before you start
- A 10x jeweler's loupe
- Digital calipers
- A gram scale
- A stopwatch or phone timer
- Reference photos of the genuine dial from a dealer listing
Step by step checks
- Measure the case with calipers. The diameter should read 41.0 mm across the case at 9 to 3 and the thickness should land near 13 mm. Replica cases often run 42 to 43 mm wide, or under 12 mm thick with a flat profile.
- Turn the watch over and study the movement through the display back. You want to see a finished automatic movement with a skeletonized rotor, Geneva stripes, and the "Probus Scafusia" engraving. A fake shows a decorated plate, a rotor with a printed logo, or a solid caseback where a display back belongs.
- Start the chronograph with the top pusher and watch the counters. The 30-minute totalizer at 12 should advance in steps while the running seconds at 6 sweep. If the subdial at 6 ticks once per second instead of sweeping, the watch holds a quartz module.
- Run the loupe along the edge of the applied numerals and indices. Genuine parts are polished on the sides and sit in a recess cut into the dial. Fake parts are stamped, soft at the corners, and sit on top of the dial surface.
- Read the printed text. "IWC" and "SCHAFFHAUSEN" are sharp, level, and spaced to match reference photos. Fakes show thick ink, crowded letters, and baselines that drift across the dial.
- Press the pushers again. Start, stop, and reset should each give a firm click with no grit and no lag. Replica chronographs built on a modified 7750 feel mushy, and the reset hand often sticks short of zero.
- Inspect the hands against the printed track. Genuine leaf hands are polished, carry a crisp center crease, and reach the minute track. Fake hands are thicker, duller, and stop short of the track.
- Read the caseback engraving and the serial between the lugs. Stamps are cut deep with clean edges. Laser-printed numbers look flat, gray, and shallow.
- Weigh the watch on the gram scale. A steel bracelet version sits in a narrow range. A fake with a hollow bracelet and light end links reads well under it.
- Compare the serial on the warranty card with the number between the lugs. Mismatched numbers mean a swapped caseback or a stripped kit put together from mixed parts.
- Time the rate over 24 hours. A healthy 69355 runs within a few seconds a day. A cheap fake drifts 20 seconds or more and the chronograph second hand stutters at start.
Red flags that end the deal
- Photos taken from a catalog instead of the actual watch
- No movement photo with the caseback exposed
- A date window or a third subdial that does not belong to the reference shown
- A price far under the going rate for a steel Portugieser on a bracelet
- A seller who refuses a video call with the watch running
If you already bought a fake
Stop the payment if you can, then report the listing to the platform and to your card issuer. Selling or importing counterfeit watches is illegal in the United States, and shipments get seized at the border. Keep the listing screenshots, the chat history, and the tracking number. Those files carry the claim with a chargeback and with a customs report.