Quick answer
The IW371650 is an IWC Portugieser Chronograph Classic. A fake shows up in three places: the movement seen through the sapphire case back, the case back engraving, and the dial printing. Genuine watches run IWC Calibre 89361. Most copies use a Valjoux 7750 or a Seagull ST19. The 7750 puts running seconds at 9 o'clock. The real watch puts them at 6 o'clock. That single difference settles most cases.
What the reference covers
The 3716 family is the Portugieser Chronograph Classic. Case width is 42 mm. Thickness is about 14.5 mm. Water resistance is 3 bar. The dial carries two counters: a combined hour and minute totalizer at 12 o'clock and small seconds at 6 o'clock. A date window sits at 3 o'clock. IWC built the line around its own 89361 movement, not a bought-in ebauche.
Reference suffixes cover dial color, case metal and strap. IWC no longer lists every 3716 variant on its current site. Confirm a specific suffix against IWC service records before you treat it as proof.
Movement
Calibre 89361 is automatic. It runs at 28,800 vibrations per hour, or 4 Hz. Power reserve is 68 hours. It has a flyback chronograph function and 38 jewels. A genuine watch beats 8 times per second, so the seconds hand moves in small steps with no stutter.
Signs of a substitute movement:
- Running seconds at 9 o'clock instead of 6.
- A 30-minute counter at 12 instead of a combined hour and minute counter.
- Rotor engraving that reads Valjoux, ETA or a Seagull code.
- Power reserve closer to 40 hours than 68.
- Chronograph pushers that feel soft or grind.
Case back and engraving
The 3716 has a sapphire display back. You should see Geneva stripes, blued screws and a signed rotor. Engraving on the outer ring is laser-cut and even. Letters have sharp inner corners. Fakes show shallow, rounded letters, uneven spacing, or a reference number that does not match the movement inside.
Check the serial number on the case back against the paperwork. A mismatch is a stop sign.
Dial, hands and crystal
Numerals are applied, not printed. Each one sits flat on the dial with a sharp edge and no glue line. The minute track is printed with clean, even strokes. Leaf-shaped hands have polished bevels and a flat top surface. The crystal has anti-reflective coating on both faces, so the dial stays readable at steep angles. Many copies coat one face and look milky from the side.
How to verify
- Take the watch to an IWC service center or a watchmaker with a timing machine. A 4 Hz reading plus a 68-hour reserve test confirms an 89361.
- Ask for the original box, warranty card and receipt. The card should carry the reference and case number.
- Compare the case number on the back with the number on the card.
No online photo test replaces a hands-on inspection. If a seller refuses to let a watchmaker open the case, walk away.