Short answer

IW371788 is not a reference number in IWC's published catalog. The IW3717 block holds Portugieser Chronograph references such as IW371701 and IW371713. A listing that uses IW371788 is a typo, a misread case code, or a number the seller invented. Ask for a photo of the caseback engraving before you send money.

What the real IW3717 line is

The Portugieser Chronograph ref. IW3717 measures 40.9 mm across and 12.3 mm thick. It runs calibre 79350, a Valjoux 7750 base with a 44 hour power reserve and 28,800 vibrations per hour. The dial carries a 30 minute totalizer at 12 and running seconds at 6. Sapphire covers the dial and the caseback. Water resistance is 3 bar. IWC replaced this line with ref. IW3716 and the in-house calibre 69355, rated at 46 hours.

Checks on a replica

  • Thickness. Measure with a caliper. Replica cases for this model run 13.5 mm to 14.5 mm.
  • Subdial axis. The 12 and 6 counters must sit on one vertical line through the crown.
  • Date font. Compare the numeral shape with a photo of a genuine dial.
  • Movement. A 7750 clone spins its rotor one way and gives a small wobble on the wrist. The real 79350 does the same. Look at rotor engraving and finish under a loupe.
  • Pushers. Start, stop and reset should click with no grit.
  • Caseback text. Deep engraving with sharp edges. Laser print sits flat and shallow.

Grade words sellers use

"First copy", "1:1" and "super clone" are trade words, not standards. No body certifies them. A quartz model under $100 has a stepping second hand. An automatic model in the $250 to $500 range most often carries a 7750 clone with a working chronograph. A higher price buys case finishing and dial print, not a different movement.

Ask the seller

  1. Which reference is engraved on the caseback?
  2. Case diameter and thickness, measured with a caliper.
  3. Movement name and beat rate.
  4. Macro photos of the caseback, clasp and crown.
  5. Return policy in writing.

Legal and value notes

A replica is not an IWC product. IWC will not service it. Resale value sits near zero. US Customs can seize counterfeit goods under 19 CFR 133. The IWC warranty does not apply to a watch with a replica serial number. Treat the purchase as a cash cost, not an asset.