Short answer

A fake IW371487 is a counterfeit copy of an IWC Portugieser Chronograph from the 3714 reference family. The genuine watch runs IWC caliber 79350, a reworked Valjoux 7750 with chronograph minutes at 12 o'clock, running seconds at 6 o'clock and a date window at 3 o'clock. Many fakes get the dial layout wrong, or they hide a stock 7750 under the caseback and leave a third subdial. Check four things: movement, subdial layout, caseback engraving and beat rate.

What the IW371487 reference covers

IWC groups IW3714 numbers under the Portugieser Chronograph. The reference changes with dial color, case metal and bracelet. IWC publishes the case metal, dial finish and strap for each number on its own site. Confirm the 371487 combination there before you compare any watch. Spec sheets for regional and limited numbers are hard to find outside auction records, so treat unverified data with care.

Movement

Caliber 79350 beats at 28,800 vibrations per hour, or 4 Hz. Count the balance or watch the seconds hand. A 21,600 vph movement, 3 Hz, shows a slower sweep. Low end replicas use the Seagull ST19 hand wound chronograph, which has no rotor. Mid tier copies use a Chinese 7750 with a rotor and a 12-6-9 subdial layout. Makers then add a fake plate over the 9 o'clock subdial or move the hands with a module. Both leave gaps in the dial cutouts that show in daylight.

Dial and hands

Genuine dials use applied numerals, a sunburst or matte finish, leaf shaped hands and a printed minute track. Look at the date window. IWC cuts it flush and matches the aperture to the dial color. Copies show a white plastic date ring, a punched hole with rough edges, or a date that sits deep under the crystal. The crystal should be sapphire with anti reflective coating on both faces. Under a lamp, sapphire shows almost no reflection at an angle. Mineral glass shows a strong blue or green flare.

Case and caseback

A steel 3714 case measures about 40.9 mm across, without the crown. Genuine casebacks carry the reference number, the individual serial number and the model name, laser etched at the same depth. Fakes use stamping. Stamped text has rounded edges and shallow relief. Compare the font weight of the numerals. IWC uses one engraving style across the line. Also check the lug width and the crown. A 3714 crown has a set number of flutes and a polished cap. Copies ship with crowns that sit too tall or turn with grit.

Price and paperwork

Pre owned steel 3714 Portugieser Chronographs trade in the low to mid four figures in US dollars. Any offer far below that range points to a replica or to a watch with swapped parts. Boxes and papers get copied, so paperwork does not prove origin. IWC service centers open a watch, check the movement and issue a report. That is the one check that settles the question.

What photos cannot show

Photos hide movement finish, caseback depth and crystal coating. A seller who sends studio images and refuses a photo of the movement and serial leaves the answer open. Ask for a 10 second video of the chronograph start, stop and reset. Genuine 79350 pushers have a firm click and reset to zero with one press.