Short answer

Ref. IW371436 is an IWC Portugieser Chronograph. People searching "fake IW371436" usually fall into two groups: buyers looking at a replica of that reference, and owners trying to work out whether a watch sold as genuine is actually a fake. The checks are the same for both. Dial printing, subdial position, caseback engraving, crown and pusher feel, and the movement under the caseback settle nearly every question.

Blunt version: a decent replica of a Portugieser Chronograph can survive a photo at arm's length. It rarely survives a loupe, and it almost never survives a movement inspection.

Confirm the reference first

Before you judge any detail, pin down what IW371436 is supposed to be. Reference numbers in the Portugieser line group by case material, dial finish, and strap, so two watches can share a case and differ everywhere else. Pull the spec sheet from IWC or a reference database and compare case diameter, lug width, crystal type, and strap option. A watch that is 2mm off, or that has a display back where the original had solid steel, is finished before you look any closer.

Dial and hands

• Printing: genuine text is level and consistent in stroke weight across the IWC and Schaffhausen lines. Replicas thicken strokes, blur serifs, and let the two lines drift out of alignment.
• Subdials: on a two-register Portugieser chronograph the subdials sit on a strict vertical axis, spaced by the geometry of the movement. Cases built around a generic chrono clone often push them off center or crowd them toward the middle.
• Hands: leaf hands should be flat on top with polished flanks and a sharp edge between the two. Look for lazy lume fill, uneven bluing, and a chrono seconds hand that will not land on 12 after a reset.
• Markers: applied numerals sit flush and cast a clean shadow. Glued replica markers tilt, sit proud, or leave a ring of adhesive.

Case, crown, and pushers

Case finishing is where cheap replicas give themselves up. Genuine Portugieser cases have firm transitions between brushed and polished surfaces, sharp lug edges, and a bezel polished to the same standard all the way around. On replicas the brushed grain runs the wrong way, edges round over, and polished surfaces show waves under a point light source.

Then work the pushers. Genuine ones travel a short distance with a firm click at start and stop, and a bit more resistance on reset. Long, mushy travel with a spongy reset usually means a low-grade module or a quartz movement hidden behind a decorated plate.

Caseback and engraving

Reference number, case number, and the IWC script on the caseback are engraved, not printed. Real engraving has depth and a faint burr at the cut edges under magnification. Laser etching looks shallow and matte. Mistakes cluster here: wrong reference format, case numbers that do not match the paperwork, or a caseback naming a movement the watch does not contain.

The movement is the decisive test

The genuine caliber in this family is a Valjoux 7750 base that IWC reworked into cal. 79350 with a two-register layout. That detail matters. The 7750 is a three-register movement, so the real watch uses a modified chronograph train. A replica that simply drops in a stock 7750 clone shows the wrong subdial arrangement, leftover date hardware, or a rotor that spins with a coarse grind. A quartz fake announces itself the moment you press a pusher: instant snap, no winding feel, no rotor sway.

If you can get the watch on a timegrapher, do it. Rate, amplitude, and beat error tell you more in ten seconds than an hour of staring at a dial.

What a replica can and cannot fake

Photo-level detail is a solved problem. Weight on the wrist, engraving depth, movement finishing, and the tactile response of the crown are not. That gap is what you are actually paying for at either end of the market, so decide which of those you care about before you spend.