Short answer

A real IW371436 is a 40.9 mm stainless steel Portugieser Chronograph with an IWC calibre 79350 inside. Copies give themselves away in four places: the size and thickness of the case, the way the two subdials behave when you run the chronograph, the quality of the applied numerals and the printing, and the movement visible through the back. If you only have thirty seconds and a photo, those four checks settle most questions.

What the reference actually is

The IW371436 belongs to the 3714 family, the Portugieser Chronograph IWC built for about two decades. Steel case, 40.9 mm across the bezel, around 12.3 mm thick, 30 m water resistance. Silver plated dial, gold plated leaf hands, applied numerals, black alligator strap. Inside sits calibre 79350, a Valjoux 7750 base running at 28,800 vibrations per hour with about 44 hours of reserve, a 30 minute counter at 12 and small seconds at 6.

Know those numbers before you look at anything for sale. A listing that says 43 mm or 14 mm thick is not describing this watch.

Case size and thickness first

This is the fastest filter. A 40.9 mm case wears like a dress watch with presence. It does not swallow a 7 inch wrist. Fakes of the 3714 tend to come out at 42 or 43 mm because the movement inside is thicker and the case has to grow around it. Put a caliper on it when you can. If a seller will not put a caliper on it, that tells you something too.

Tap the case. It should feel dense and thin for its size, not hollow.

Run the chronograph

Start it, stop it, reset it. On a quartz copy the big seconds hand ticks once per second and the subdials often do nothing at all. On a cheap mechanical copy the pushers feel soft, the 30 minute counter stops advancing after a few minutes, or the reset leaves the hand parked off zero. A real 7750 based chronograph has firm pushers with a clear click and a snap back to 12 that lands dead center.

Dial and hands

Look at a numeral from the side. Applied markers stand off the dial and throw a thin shadow. Printed ones sit flat. Under a loupe, IWC's printing is tight, with even spacing and clean letter edges. Copy dials run thicker and slightly fuzzy, and the gap between the IWC letters is often wrong. Subdial rings should be recessed and finished with fine concentric lines. Hands should be polished on every facet, and blued steel should read blue-black, not painted blue.

The sweep is a giveaway as well. A 28,800 vph movement beats eight times a second, so the chronograph seconds hand glides. Four or five visible steps per second means a slower movement inside.

The caseback and the movement

Reference and serial numbers are engraved into the metal, deep and crisp, with sharp edges. Laser etching looks shallow and grey next to that. Where there is a sapphire back, the movement should show decoration: striped or circular grained bridges, blued screws, a signed rotor with correct fonts. Copies often show a bare movement with a plastic spacer ring, or rotor engraving that looks close until you set it beside a photo of the real thing.

Strap, buckle, and the boring details

Alligator with square scales and a signed buckle or deployant. Copies arrive on embossed leather with a generic buckle or a clasp that rattles. Check the crown too. It should screw and unscrew without grit, and setting the date should feel positive.

Price and paperwork

Used examples of the IW371436 trade in the mid four figures on the open market, more with full box and papers. There is no version of this reference selling for a few hundred dollars. Service receipts and an IWC extract help, and a seller who is happy to meet at a watchmaker for a movement check is a seller worth dealing with.

If you want a copy anyway

Plenty of people buy this reference for the look rather than for the movement. Judge a copy as a copy. Ask what movement is in it, whether the chronograph counts real minutes, the exact diameter and thickness, and whether the dial uses applied markers. A good copy of the 3714 layout lands between 40 and 41 mm and around 13 mm thick, with a working 30 minute counter and a hand that resets clean. Anything vaguer than that is a gamble.

Bottom line

Measure the case, run the chronograph, look at the print and the numerals from an angle, then get a look at the movement. The IW371436 is a simple, honest watch, and that is exactly why copies are easy to catch.