Short answer
A fake IW371740 is a counterfeit of an IWC chronograph from the 3717 series. The genuine watch has a 42 mm steel case, a day and date window at 3 o'clock, three subdials, and IWC calibre 79320. Retail price during the production run was about $5,900 USD. Copies sell from $80 to $500. Most copies match the case outline and fail at the movement. A watchmaker can confirm the answer with a caseback tool and a timegrapher.
What the reference is
IWC built the 3717 series from 2006 to 2012. The line covers Pilot's Watch Chronograph and Spitfire Chronograph models. Reference suffixes such as IW371740 mark case metal, dial color, and strap. IWC does not publish a full list of every suffix, so a suffix that appears in a listing and not in a catalog is not proof by itself.
Core specs: 42 mm case, sapphire crystal front and back, calibre 79320, 28,800 vibrations per hour, 44-hour power reserve, day and date at 3 o'clock.
Where copies fail
Movement
Calibre 79320 is a modified Valjoux 7750. It beats 28,800 times per hour. The small seconds hand at 9 o'clock moves in 8 steps per second. Copy movements include the Seagull ST19 at 21,600 vph, which is 6 steps per second, and undecorated Asian 7750 clones. A phone video at slow speed shows the step count. A timegrapher gives the rate as a number. A reading of 21,600 points to a copy.
Caseback
Genuine 3717 watches have a sapphire display back. The rotor carries IWC engraving and finishing. Copy rotors show a plain surface, a 7750 stamp, or engraving that sits shallow and off-center. Reference and serial numbers on the caseback edge sit in a straight line with even depth.
Dial and glass
Genuine sapphire has anti-reflective coating on the inner face. A blue or purple tint shows at an angle. Copies use mineral glass with no coating, or coating on the outside that wears off. Applied indexes sit flush on the genuine dial. Lume plots on copies sit high and show gaps at the edges.
Day and date
IWC matches the day and date wheel color to the dial on most 3717 variants. Copies often use a white wheel on a black dial. Compare stroke width and font to photos of the same reference.
Price test
No genuine IWC chronograph sells for $200. Listings at that level are copies, quartz replicas, or watches with swapped movements. A used 3717 sells for $3,500 to $5,000 from a dealer with papers. A price under $1,000 with a claimed box and papers fails the test.
How to verify
- Open the caseback at a watchmaker and read the calibre stamp.
- Run the watch on a timegrapher. A rate of 21,600 vph points to a copy movement.
- Send the serial number to an IWC service center. IWC does not run a public serial database.
- Compare caseback engraving depth and font against photos from IWC.
These checks apply to other brands with display backs. The movement and the price carry more weight than the case finish.