The best fake IW371427 is the top-tier version with a working chronograph movement, a steel case within a millimetre of the real 40.9 mm, a sapphire crystal, and dial print that survives a loupe. That is the pick worth paying for, and everything under it gives up one of those four things. The criteria used here are the ones that decide whether a copy reads as a watch or as a prop: case diameter and thickness, movement type and whether the chronograph runs, dial and hand finish, crystal material, and the strap or bracelet.

What ref. IW371427 actually is

IW371427 belongs to the IWC Portugieser Chronograph line. The case is stainless steel at about 40.9 mm across and about 12.3 mm thick, with a sapphire crystal and a display back on most production years. The dial carries two registers: a chronograph minute counter at 12 o'clock and running seconds at 6. Hands are leaf shaped and the numerals are applied. Water resistance is rated at 3 bar, which covers splashes and nothing more. Movements changed across production years, so anyone verifying specs should check the exact reference on IWC's own product page instead of trusting a seller's photo.

The three replica tiers, compared

Entry tier: quartz or dummy chronograph

  • Pros: lowest cost, light on the wrist, correct silhouette from across a room.
  • Cons: pushers do nothing or the sweep ticks, case runs 2 mm thick, mineral glass, soft dial print, wrong date font, thin strap.

Buy this only as a novelty. Nothing about it survives close inspection.

Mid tier: automatic with a 7750-derived chronograph

  • Pros: the chronograph actually runs with the right 12 and 6 layout, automatic winding, sapphire on many examples, dial print that holds up at arm's length.
  • Cons: case often 1 to 2 mm too thick, audible rotor, date window slightly off position, bracelet edges left sharp.

This is the value tier for someone who wants a functioning two-register chronograph and can live with a case that sits taller than the original.

Top tier: dimension-matched copy

  • Pros: case close to spec, correct dial font weight and spacing, anti-reflective sapphire, crisp pusher feel, strap stitching that matches the reference.
  • Cons: highest price, no service network, uneven supply, and a good tier can still ship a poor unit.

Pick this if case proportions and dial accuracy are the whole point of the purchase.

Criteria that separate a good copy from a bad one

  1. Case dimensions. 40.9 mm wide and about 12.3 mm thick. One millimetre of extra thickness changes the whole profile.
  2. Chronograph function. The minute counter must sit at 12 and advance in steps. A sweeper or a frozen subdial is the fastest tell.
  3. Dial print and hands. Look at the weight of the numerals and whether the leaf hands have a polished bevel.
  4. Crystal. Sapphire with coating. Mineral glass shows a grey haze at an angle.
  5. Strap and clasp. Alligator-grain leather with even stitching, or a bracelet with clean end links.
  6. Movement finish. Ranked last because it sits behind a caseback, but a rough rotor is a rough watch.

Checks to run the day it arrives

  • Measure the case with calipers before you wear it.
  • Start the chronograph and watch the 12 o'clock counter step forward.
  • Set the date forward and back to confirm it snaps instead of drifting.
  • Inspect dial print under a loupe for bleed and uneven spacing.
  • Tilt the crystal under a lamp to check for distortion.
  • Flex the strap and feel the clasp for burrs.

Legal and practical notes

Counterfeit watches are illegal to import and sell in the United States and across most of Europe, and customs seizures happen often. Trademark holders pursue sellers, and marketplaces remove listings on complaint. A replica also carries no warranty and no service path. Many watchmakers will decline to open one, and a failed movement can be hard to source, which turns a cheap watch into a disposable one.

Which tier fits which buyer

If the goal is a beater that reads correctly from across a table, take the entry tier and accept that it is costume. If a running chronograph matters, the mid tier is the sensible stop. If case proportions and dial accuracy matter more than anything else, the top tier is the only one that answers. If resale value, servicing, or paperwork matters at all, skip all three and put the money toward the real reference.