Short answer
IW371633 is a reference number in the IWC Portugieser Chronograph line. The watch has a 41 mm stainless steel case, two subdials, no date window, and calibre 69355 inside. A fake IW371633 is any watch sold under that number that IWC did not build. Copies match the silhouette. They miss the movement, the crystal, and the case finishing.
The digits after 3716 are not tied to a public rule. IWC assigns them to dial, strap, and market combinations. Confirm IW371633 against an IWC dealer, the warranty card, or the IWC catalog before you accept or reject a watch.
Factory specs to compare
- Case: stainless steel, 41.0 mm wide, 13.1 mm thick
- Movement: IWC calibre 69355, automatic, column wheel chronograph
- Rate: 28,800 vph (4 Hz), 46 hours power reserve
- Crystal: domed sapphire, anti-reflective coating on both faces
- Water resistance: 3 bar
- Dial: small seconds at 6, chronograph minutes at 12, no date
- Hands: leaf shape, applied Arabic numerals
These figures describe the 3716 family. Dial color, strap, and case material change with the last digits of the reference.
Movement is the first check
Calibre 69355 runs a column wheel. The rotor winds in both directions. A Valjoux 7750 based copy uses a cam and lever system and winds one way. Both run at 28,800 vph, so beat rate alone proves nothing. Look at the rotor engraving, the balance bridge shape, and the surface finish. Many replicas use a decorated 7750 with an added rotor plate.
Dial and case details
Applied numerals on the real watch sit above the dial with polished edges. Printed numerals on a copy sit flat. Counter position follows the base movement: a 7750 places its two counters at a fixed spacing. If the counters sit closer or wider than IWC catalog photos, the movement is not 69355.
Pushers at 2 and 4 are round and sit flush. The case back ring carries the reference number and a case serial. Shallow etching, uneven depth, or a font that differs from IWC stamping points to a copy. A chrome-plated brass case weighs less than steel. A kitchen scale settles that question.
Crystal and finishing
Sapphire on the genuine watch is domed and coated on both sides. Hold the watch under a lamp: coated sapphire shows a faint blue or purple tint, mineral glass shows a white glare and scratches against a steel key. Case flanks on the real watch carry a brushed surface, polished bevels, and sharp transitions. Copies round the bevel or leave tool marks near the lugs.
What photos cannot settle
Photos cannot confirm a movement, a serial, or service history. Ask for a timed run of the chronograph. The seconds hand should start with no jump and reset to zero. Ask for the case back photo, the warranty card, and the seller invoice. IWC does not publish a buyer-facing serial lookup, so a dealer or service center check settles it.
Checklist before you judge a watch
- Case back photo with reference and serial
- Movement photo, full frame, rotor and balance visible
- Dial macro shot at 12 and 6
- Lug and bevel close-up
- Weight on a scale
- Chronograph start, stop, reset
- Warranty card and purchase receipt
If a seller refuses any item on that list, treat the watch as a copy.