The short answer
If you are trying to work out whether an IW371421 is fake, start with the movement and the case measurements, not the dial. Replica makers get dials close. They get movements, tolerances, and finishing wrong far more often. On a Portugieser Chronograph, the dial is the last thing to check, not the first.
What the IW371421 actually is
IW371421 sits inside the Portugieser Chronograph family, the line most people know as the 3714. That reference number is doing real work: within the family, the digits encode a specific dial and case combination, so two watches that look nothing alike online can both be described loosely as "a 3714." Before you judge any watch, pull the exact reference from a database and compare the details one by one: dial color, numeral finish, hand style, whether there is a date, case metal, and strap.
The 3714 generation shares a common architecture. A case around 41mm across, sapphire crystal up front, a display back, two subdials placed at 12 and 6 (30-minute counter on top, running seconds below), a date aperture at 3 o'clock on most versions, and IWC's calibre 79350, which is a heavily reworked Valjoux 7750. The 2020 refresh of the line moved to the in-house calibre 69355, so treat any listing that calls a 3714-era watch "in-house" as a warning sign about the seller, not the watch.
Why this reference gets copied so much
It is a clean, legible, high-recognition design with a simple two-subdial layout. That makes it easier to fake convincingly than a skeleton chronograph or a complicated perpetual calendar. It also sells for enough money that a replica has a market. Those two facts together explain the volume of fakes you will run into.
Check 1: dimensions and weight
- Measure the case with calipers if you can. Replicas frequently run 0.5 to 1.5mm off, usually thick.
- Weigh it. A genuine steel Portugieser Chronograph on a leather strap lands in a fairly narrow band. A noticeably light watch usually means a thinner case or a cheaper movement.
- Check lug width and how the strap sits. Crooked spring bars and gaps at the lugs are common on copies.
- Look at the crown and pushers in profile. They should sit flush and feel tight, not wobbly.
Check 2: the movement
This is where most fakes die. Ask for a clear photo of the display back, running, with the chronograph engaged. On a 79350-based watch you want to see a well-finished automatic chronograph movement with a signed oscillating weight, correct engraving, and blued screws where they belong. Asian 7750 clones exist and can look passable at a glance, but the finishing is flatter, the rotor engraving is shallow or wrong, and the pusher feel is vague. Start and stop the chronograph. A healthy 7750 family movement snaps. A tired clone mushes, and the reset hand often does not return perfectly to zero.
Check 3: dial and printing
Use a macro photo from an official source and compare at high zoom. Look at the sharpness of the text, the weight of the minute track, the shape of the feuille hands, and the finish on the numerals. Replica printing tends to be slightly thick or slightly soft, and the subdial rings are often a fraction too wide. Subdial position is worth measuring too: they should sit at 12 and 6 with even spacing from the center, not shifted toward the middle.
Check 4: case, crystal, and caseback
Genuine sapphire has a faint blue or purple edge reflection under certain light. Cheap mineral glass reads differently, and it scratches easily. On the caseback, the reference number, case number, and model engraving should be crisp and evenly spaced, not laser-fuzzy. Look at the caseback screws, the brushing direction, and the polish on the bezel. Mixed or inconsistent finishing is one of the most reliable tells.
Check 5: strap, buckle, box, papers
A genuine watch usually arrives with a strap that has clean stitching, even thickness, and a signed buckle with correct proportions. Fakes often ship with a stiff strap and a buckle that is too thick or has a soft logo. Boxes and papers are easy to fake, so never treat them as proof. A complete set with mismatched serials is a bigger red flag than a watch sold alone.
Questions worth asking a seller
- Can you send a photo of the caseback engraving and the movement running?
- What is the exact reference, and which dial variant is it?
- Do you have a service record, and who serviced it?
- Will you accept a return if a watchmaker confirms the watch is not genuine?
- Do the case and movement numbers match what IWC would have paired?
Any hesitation on the first two questions usually ends the conversation for me. A real owner can produce those photos in ten minutes.
The money side, and the law
Counterfeit branded watches cannot be serviced by the brand, hold no resale value, and in the United States and most of Europe selling them is illegal. Buying for personal use is treated differently from place to place, and in some countries it is a criminal matter. That matters less as morality and more as math: a fake is a disposable object, a genuine watch is not.
Bottom line
Check the movement first, then the case measurements, then the dial. If the movement is right and the case is the correct size and weight, almost everything else will fall into place. If either one is off, no amount of clean printing will save it.