The short answer
A fake IW371446 is a copy of the IWC Portofino Chronograph, and the tells cluster in five places: the case back engraving, the chronograph pushers, the day and date window alignment, the dial printing, and the movement you can see through the back or feel at the crown. Genuine examples carry crisp machine engraving, a Valjoux based caliber 79320, and a 42 mm steel case with the same brushed and polished transitions on every example. Copies miss at least one of those marks.
What the reference should be
IW371446 is a stainless steel Portofino Chronograph with a black dial on a black alligator strap. Confirm the exact spec on the official IWC reference page before you judge any watch, because the same base number covers dial and strap variants. Expect a 42 mm case, sapphire crystal, a chronograph with two subdials, a day and date display, and an automatic movement with roughly 44 hours of power reserve.
Before you start
- A 10x loupe or a phone macro lens
- Bright light you can angle across the case
- The official IWC spec sheet for IW371446 open for comparison
- A caliper, if you can borrow one
- Photos of the watch in question from at least four angles
How to check an IW371446 step by step
- Measure the case across the widest point, excluding the crown. A genuine Portofino Chronograph is 42 mm. Copies often run 40 mm or 43 mm.
- Inspect the case back engraving under the loupe. Genuine IWC engraving has sharp, even walls and frosted interiors. Fake engraving looks shallow, rounded, or filled with black paint.
- Read the reference number on the back. It must read IW371446, and the digits must match the dial and strap combination you were shown.
- Press the chronograph pushers. Genuine Valjoux based movements start, stop, and reset with a firm click and a snappy return to zero. Cheap quartz and low grade automatic copies feel mushy, and the reset hand drifts.
- Watch the running seconds subdial. On a genuine automatic it sweeps in small steps. On a quartz copy it ticks once per second.
- Check the day and date windows. The discs should sit level in the aperture with no cut off letters, and the day should change cleanly at midnight.
- Study the dial text. "IWC" and "SCHAFFHAUSEN" should be crisp, level, and evenly spaced. Look for thick, bleeding, or misaligned print.
- Inspect the hands and subdial rings. Genuine hands are polished on the top edge and matte on the side. Copies leave rough edges or uneven lume.
- Weigh the watch by hand. A steel Portofino Chronograph feels dense for its size. A light, hollow feel points to a plated brass case.
- Compare the crystal at an angle. Sapphire shows almost no reflection. Mineral glass throws a blue or purple sheen and scratches with a light pass of a pin in an inconspicuous spot.
- Inspect the strap and buckle. Genuine alligator has irregular scale patterns, and the signed buckle carries clean engraving.
- Ask for a photo of the movement with the case back removed, then compare the rotor engraving and finishing against reference images of caliber 79320.
Common red flags
- A price far below the normal range for the reference
- A seller who refuses an in person inspection or third party authentication
- A reference number on the back that does not match the dial layout
- Papers whose fonts differ from the printing on the watch itself
- The same serial number appearing in more than one listing
Verify before you buy
No single check settles the question on its own. Two or three mismatches together are enough to walk away. If you cannot inspect the watch in person, pay for third party authentication and use an escrow style payment. Save the seller's photos, because they document the watch as it was described to you.