Answer first

IW371673 is an IWC Portugieser Chronograph. The 3716 family uses a 41 mm case, a sapphire crystal, and IWC calibre 69355, an automatic chronograph with about 46 hours of power reserve at 28,800 vibrations per hour. Fake versions of the Portugieser line appear on marketplaces, and most fail at the same four points: the movement and caseback, dial printing, case finishing, and the paperwork.

One check tells you little. Three checks that fail tell you a lot.

What the reference number tells you

IWC reference numbers carry a family code and a variant code. IW3716 is the Portugieser Chronograph family. The final digits mark the dial and case variant. A seller who names a reference but shows a photo of a different dial has given you the first answer. Ask for the reference number engraved on the caseback and compare it to the number in the listing and on the warranty card. All three should match.

Confirm the current specification for this reference on the IWC product page. Dial colors and strap options change between variants.

Movement and caseback

  • The 3716 has a display back. A solid steel back on a watch sold as this reference is a stop sign.
  • Calibre 69355 is an IWC automatic chronograph. The rotor and bridges carry IWC engraving and the calibre number.
  • Look at the finish on the bridges and the rotor. Genuine IWC uses Geneva stripes, perlage, and blued screws. Copies use printed plates or rough brushing.
  • Fakes often run a Valjoux 7750 base or a Chinese copy of it. The chronograph works, but the pusher feel differs. Light engagement and a soft reset are common on copies.
  • Ask a watchmaker to open the back and check the movement. Ten minutes of bench time costs less than a bad purchase.

Dial and hands

  • Two subdials: a 30-minute counter at 12 and running seconds at 6. Copies sometimes use a three-subdial 7750 layout with a 9 o'clock subdial, or a subdial hand that does not track the correct function.
  • Printing under 12 o'clock reads IWC and SCHAFFHAUSEN. Letters should be sharp at 10x magnification. Copies show ragged edges, uneven spacing, and thick strokes.
  • Applied indices sit flat and reflect light in one line. Glued-on indices on fakes sit at an angle.
  • Leaf hands are polished, with sharp tips and a clean center line.

Case, crown, and strap

  • The caseband is brushed, and the bezel and lug tops are polished. The transition between the two surfaces is a clean line, not a blurred gradient.
  • Lug edges are sharp. Copy cases round them off.
  • The crown and pushers align with the caseband and sit flush.

Weight and feel

Weigh the watch. A kitchen scale with 1 g resolution is enough to compare against a genuine example of the same reference. Steel cases vary little between units, so a gap of more than a few grams points to a different case material or construction. Mass alone is not proof. Use it as one data point.

Box, papers, and price

Genuine IWC packaging has a printed reference and serial on the warranty card. Cards that do not match the caseback, or blank cards, are a problem. Price is the last signal. A current steel Portugieser Chronograph sells for several thousand US dollars on the secondary market. A listing far below that number is not a bargain.

What to do next

Ask for the serial and reference, photos of the caseback and the movement, and the original invoice. Send the photos to an authorized IWC service center or an independent watchmaker who services IWC. A service estimate is also an authentication check. A service center will decline or flag a counterfeit case.