Short answer

IW371780 is a reference number written in the IWC format: the letters IW plus six digits. The IW3717 block belongs to the Pilot's Watch Chronograph line. IWC catalogs list IW371701 and IW371704 inside that block. I cannot confirm that IW371780 exists as a real IWC catalog number. Treat a watch sold under that number as unverified until the digits match an IWC source.

What the IW3717 block covers

The IW3717 Pilot's Watch Chronograph uses a 42 mm steel case and IWC calibre 79320. That movement is a modified Valjoux 7750: 25 jewels, 28,800 vibrations per hour, about 44 hours of power reserve. Subdial layout runs seconds at 9, 30-minute counter at 12, 12-hour counter at 6. Day and date sit at 3. A sapphire crystal carries anti-reflective coating on both faces. The crown screws down.

Points fakes get wrong

  • Subdials that never move. Quartz copies freeze the counter at 6.
  • Case diameter off by 1 mm to 2 mm. Measure with calipers, not by eye.
  • Date wheel font. IWC numerals use thin, even strokes.
  • Rotor engraving. Real rotors carry the IWC mark and the words Probus Scafusia.
  • Crystal material. Mineral glass scratches and throws a dull reflection at an angle.

Checks in five minutes

  1. Write the full reference down. Compare it to the IWC model list and to two dealer databases.
  2. Start the chronograph. The counter at 6 should step forward in one-hour jumps.
  3. Listen to the balance. 28,800 vph equals 8 beats per second. A quartz copy ticks once per second.
  4. Inspect the case back. Reference and serial are laser engraved on genuine cases. Many fakes use shallow stamping.
  5. Ask for a movement photo. Calibre 79320 has a known rotor shape and bridge layout.

Serial numbers and papers

IWC serial numbers run in blocks and are not reused per reference. A serial that maps to a different model points to a swapped case back. Boxes, warranty cards and booklets are copied with ease. Papers prove nothing on their own. A service invoice from an IWC service center carries more weight.

Price signal

Used Pilot's Watch Chronographs trade in the low thousands of US dollars on the secondary market. Offers under that range come with a reason. Ask which one.