Short answer
Most watches sold as an "IW371787" are copies. The reference format is real: IWC numbers its watches with the letters IW followed by six digits. What appears in a listing photo is often a generic Pilot's Watch Chronograph case with a printed dial. Four checks separate a genuine 3717-series IWC from a copy: case measurement, dial print, movement beat rate, and caseback engraving.
What the number tells you
The 3717 block covers IWC's Pilot's Watch Chronograph generation sold in the 2000s. Listing data for those references shows a steel case, a day and date window at 3 o'clock, three subdials, and caliber 79320 inside. That caliber is an automatic chronograph built on the Valjoux 7750 architecture and runs at 28,800 vibrations per hour.
IWC does not publish a full public reference list. If a seller shows "IW371787" and you cannot match it to an IWC catalog page, treat the number as unconfirmed. Ask for the caseback photo and the serial number before any payment.
Checks that catch copies
- Measure the case with calipers. Copies run 1 mm to 2 mm off the catalog size, with the largest error at the lugs.
- Count the beats. Hold the watch to your ear or use a timegrapher app. Caliber 79320 runs at 4 Hz, or 28,800 vph. A quartz tick or 21,600 vph reading means a copy.
- Read the dial text. Genuine print holds a sharp edge under a loupe. Copy print shows broken strokes and uneven spacing. Check the "Schaffhausen" line and the minute track.
- Inspect the day and date wheels. Genuine wheels use one font and align flush to the window edge. Copies show off-center numbers and wide gaps at the frame.
- Look at the caseback. Genuine engraving is cut into the metal, not printed. It carries the reference, the serial, and the IWC name in a fixed layout.
- Check the crown and pushers. Pushers on copies have more travel and a loose feel at the start of the chronograph stroke.
- Weigh the watch. A steel 3717 case on a bracelet sits in a narrow weight band. Copies come in light because of hollow links or a thinner case.
Movement details
Caliber 79320 keeps a power reserve of about 44 hours, the figure tied to the 7750 base. The chronograph uses a cam and lever system, so the start press has a firm stop, not a soft mush. A display back helps here: copy movements show unfinished plates, mismatched screws, and rotor text with the wrong depth.
Price reality
Used 3717-series chronographs trade in the thousands of dollars on the secondary market. A seller asking a few hundred dollars for a steel IWC chronograph is selling a copy. Low prices are the first signal, not the last.
Before you pay
Ask for photos of the caseback, the movement, and the clasp markings. Request the service history. A watch with no papers can still be genuine, but the serial on the caseback should match the movement and the papers.