A fake IW371787 is a replica of the IWC Portugieser Chronograph, and the fastest way to judge one is to compare three things against the real reference: case size, dial layout, and the chronograph movement. Work through the checks below in order and you will know within ten minutes whether a copy is worth the money.
Baseline: what the real reference does
The IW371787 sits in the Portugieser Chronograph family. Expect a stainless steel case around 41 mm across and close to 13 mm thick, a bicompax dial with a 30-minute counter at 12 and running seconds at 6, a date at 3, leaf hands, applied numerals, sapphire crystal front and back, and 30 m of water resistance. Inside runs the in-house 69355 automatic chronograph with about 46 hours of reserve. A copy that misses these numbers is wrong before you inspect a single screw.
How to check a first copy
- Ask the seller for the case diameter measured with a caliper and a photo of the reading. Accept 40.9 mm to 41.2 mm, and reject anything outside that band.
- Ask for the thickness in the same photo set. A figure above 14 mm means a thick base case and a dial that sits too deep.
- Request one straight-on dial photo in daylight with no crop. Check that the two subdial centers sit on the vertical axis and that the date window aligns with 3 o'clock.
- Zoom the photo to the branding. The letters must have crisp edges, even spacing, and no ink bleed into the dial finish.
- Study the hands. Leaf hands with a polished bevel and a clean center sweep, not flat stamped metal with a visible seam.
- Turn the watch over. You want a sapphire caseback, engraved rotor text, and a movement layout that matches the 69355, not a generic chronograph module with an offset rotor.
- Run the chronograph. Start, stop, and reset should feel firm, the reset should snap the hands to zero in one move, and the counter at 12 should advance once per minute.
- Press the pushers and wind the crown. Grit, wobble, or a pusher that sticks halfway is a fault that appears again after a month of use.
- Inspect the strap and buckle. Stitching should run straight, the lining should be soft, and the buckle engraving should be sharp on both surfaces.
- Ask for the seller's own photos of the exact unit, not catalog shots. If the answer is silence, walk away.
Red flags that end the sale
- Subdials placed closer to the center than the genuine layout.
- Printed numerals instead of applied metal.
- A closed steel caseback on a reference that ships with sapphire.
- Chronograph seconds that stutter instead of sweeping.
- A price far under the rest of the market for the same grade.
Price and disclosure
A first copy at this level sits in the low hundreds of dollars. Pay more only when the seller shows movement photos, caliper readings, and a return window. Treat the watch as a replica in every conversation: it is not an IWC, it carries no factory warranty, and it should never be sold or gifted as genuine. Buy it as a look-alike, wear it as one, and keep the paperwork that states what it is.