The IW371743 sits in the IWC Portugieser Chronograph line. Replicas of this series are common. Most fail on parts you can check in five minutes with a loupe and a caliper. Check five points: case diameter, subdial function, movement, dial print, caseback engraving.
One note before the list. IWC lists current Portugieser Chronograph models under the IW3716 family. The 3717 series came before it. Public records for the exact 371743 suffix are thin, so confirm the case metal and dial color with IWC or an authorized dealer before you judge a watch against photos.
Case and crystal
A Portugieser Chronograph case measures about 40.9 mm across, crown excluded. Thickness runs near 12.5 mm. Replica cases come in at 42 mm or more, or run 14 mm thick, because the clone movement needs room. Measure with a caliper. Do not trust the listing text.
The crystal is sapphire with antireflective coating. Under a lamp, a real crystal shows a faint blue or purple tint at an angle. Mineral glass on a fake scratches with a steel pin and shows no coating tint.
Dial and subdials
The layout matters. The subdial at 12 counts chronograph minutes, up to 30. The subdial at 6 runs the seconds hand. The date sits at 3. If running seconds sit at 12, the watch is wrong.
Dial print reads IWC and SCHAFFHAUSEN below 12, with AUTOMATIC and CHRONOGRAPH above the 6 subdial. Check letter spacing and stroke weight. Replica print sits heavy and the letters crowd.
Applied numerals and leaf hands are polished and faceted. A loupe shows sharp inner angles. Fakes show soft edges and glue at the base of a marker.
Movement
The 3717 series uses IWC calibre 79350. That is a Valjoux 7750 base, reworked by IWC, running at 28,800 beats per hour with a 44-hour power reserve. Set the watch down for two days and it stops. A clone 7750 with a 40-hour reserve and gritty winding is a signal.
Start the chronograph, then reset it. The hands should snap back to zero in one motion. A slow crawl or a wobble points to a clone module.
Caseback, crown, strap
Caseback engraving is deep and sharp. Reference and serial numbers are laser-cut, not stamped in one flat font. Confirm the back type for this reference before you buy. Some Portugieser Chronograph examples use a solid steel back, others a sapphire display back, and a mismatch is a red flag.
The crown carries the IWC signature. Threads engage in under two turns and feel smooth. Replica crowns feel gritty or sit off-center against the case.
Original straps are alligator with a signed pin buckle or deployant. Stitching is even and matches the original pitch. Buckle engraving matches the caseback in depth.
Price and paperwork
A steel Portugieser Chronograph trades in the thousands of dollars on the secondary market. A listing at a few hundred dollars is not a bargain. Ask for the warranty card, the box, and the service history. Call an IWC boutique or service center with the serial number. IWC will confirm a service record. It will not confirm authenticity over the phone.
What photos cannot show
Weight, winding feel, and pusher resistance need the watch in hand. Ask for a video with sound, a photo of the caseback under raking light, and a caliper shot. A seller who refuses all three is telling you something.