The top pick for most buyers is an automatic fake IW371620 built on a 41 mm case with the two registers at 12 and 6 and a chronograph that actually runs, because that combination is the only tier that gets the silhouette and the mechanical feel anywhere near the genuine Portugieser Chronograph. The criteria that decide everything else are case size and thickness, dial printing and register spacing, the movement under the caseback, and the crystal and engraving. Each of those checks is covered below, along with the tier that suits a given buyer.

What the genuine IW371620 sets as the baseline

Reference IW371620 sits in the 3716 family of the Portugieser Chronograph. IWC builds that family around a 41 mm stainless steel case, the in-house calibre 69355 with a column-wheel chronograph, a 46-hour power reserve, sapphire crystal, and a water resistance rating of 3 bar. Dial colour and strap differ between references inside the same family, so confirm the exact configuration listed for IW371620 against the manufacturer's reference data before you treat it as your yardstick.

  • 41 mm case diameter, roughly 13 mm thick
  • Two registers: 30-minute counter at 12, running seconds at 6
  • 3 bar water resistance, which is splash and rain protection only
  • Sapphire crystal with anti-reflective treatment

Those figures matter to a replica buyer because they are the ones you can verify with calipers, a loupe, and a phone macro shot.

Criterion: case size and thickness

Diameter is easy to copy and thickness is not. A build that measures 41 mm across the bezel will still look wrong if it stands 14.5 mm tall, because the extra millimetre sits in the mid-case and pushes the lugs off the wrist curve.

  • Pros of a correct-profile case: lugs sit flush, the watch slides under a cuff, the bezel-to-dial ratio matches the reference, and the pushers line up with the crown at 3.
  • Cons of a swollen case: the crown guards look blunt, the caseback stands proud, and the whole watch reads as a generic chronograph rather than a Portugieser.

Measure lug tip to lug tip, not just across the bezel. A case that is right in diameter but wrong in lug length will leave a gap at the spring bar and a visible seam against a strap.

Criterion: dial, subdial spacing, and printing

Register placement is a function of the movement underneath, which is why it is the hardest thing for a cheap build to hide. The 12 and 6 stack has to sit on the vertical centre line, with the counters sized identically and the outer track running true through both.

  • Pros of a well-printed dial: applied indices catch light on their polished edges, the minute track does not crowd the registers, and the subdial hands reach their marks.
  • Cons of a budget dial: misaligned counters, printed rather than applied markers, blotchy lacquer, and a date aperture with no frame where the reference has one.

Check the subdial spacing first with a straight edge laid across the dial. If the two registers sit wide of centre, the movement is a different architecture and no amount of dial work will fix it.

Movement tier: quartz builds

Quartz versions are the entry point and the most common source of disappointment.

  • Pros: thin, light, keeps time without winding, and costs the least.
  • Cons: the small seconds hand ticks instead of sweeping, pushers feel dead when pressed, and the 12 o'clock counter is often decorative rather than functional.

Buy this tier only if the watch is a costume piece you will wear a few times a year. It will not survive close inspection at arm's length.

Movement tier: automatic chronograph builds

This is the tier most buyers should aim for. An automatic chronograph movement with the right register layout gives you a sweeping seconds hand, functioning pushers, and the correct case weight.

  • Pros: correct 12 and 6 register layout, working start-stop-reset, exhibition caseback that shows real parts, and a rotor that spins with wrist movement.
  • Cons: thicker case than the reference, more expensive to service, and the engraving on the rotor rarely matches factory text.

Ask for a video of the chronograph being started, stopped, and reset before you commit. A functioning zero reset is the single best proof that the movement is not a dressed-up quartz.

Movement tier: higher-grade automatic with finishing

At the top of the replica market you get perlage and Geneva stripes on the bridges, blued screws, and a properly engraved caseback.

  • Pros: closest visual match through a display back, better tolerances on the crown and pushers, sharper dial finishing.
  • Cons: the price gap over a standard automatic buys cosmetics, not accuracy, and the resale market for these builds is thin.

Choose this tier if you wear the watch with the caseback visible or you handle it often. Skip it if the back stays against your wrist.

Authentication checks that flag a fake IW371620

Run these in order when a watch is handed to you as the real thing.

  1. Measure the case. Anything over roughly 13 mm thick needs a second look.
  2. Lay a straight edge across the dial and confirm the registers sit on the centre line.
  3. Start the chronograph and watch the reset. A snapping instant return points to a mechanical movement.
  4. Inspect the crystal at an angle. Anti-reflective treatment on both faces gives a faint blue or purple cast.
  5. Check the caseback engraving with a loupe. Fonts, spacing, and reference digits are the usual weak point.
  6. Verify the water resistance claim. A 3 bar rating is splash protection, so a seller describing it as safe for swimming is handing you a warning sign.

None of these checks requires opening the watch, and together they will separate a serious build from a throwaway one.

Which build fits which buyer

A first-time buyer on a tight budget should take a quartz piece and treat it as a test of whether the size suits their wrist. A daily wearer should take the automatic chronograph tier with a functioning reset and a correctly spaced dial, since that is where the watch stops looking like a placeholder. A collector of replica builds should go one step up, where the finishing and engraving hold up under a loupe. In every case the order of priority stays the same: case profile first, dial and register spacing second, chronograph function third, cosmetics last.