Answer First

The IW371621 sits inside the IWC Portugieser Chronograph 3716 family. The genuine watch uses a 41 mm stainless steel case that is 13.1 mm thick, 20 mm lugs, sapphire crystal on both sides, a two-register chronograph dial, and a date window at 3 o'clock. Inside runs the in-house calibre 69355 with a column wheel and roughly 46 hours of power reserve. A replica IW371621 copies that shell and swaps in a third-party movement. Assembly, dial printing, and case finishing decide whether the copy reads as a watch or as a costume piece.

Dial color, hand finish, and bracelet versus strap change with the exact variant, so pull official product photos of your reference before you compare anything. Small details differ between the sub-references in the 3716 line.

Before You Start

  • Digital calipers, for case and lug measurements.
  • A 10x loupe, for dial printing and hand finishing.
  • A timegrapher or a phone timing app, for rate and beat error.
  • Official photos of the reference, printed or on a second screen.
  • A written return window from the seller, in days, not promises.

Inspection Steps

  1. Measure the case across the bezel with calipers and compare to 41.0 mm. A copy that lands 1 mm wide sits wrong on the wrist.
  2. Measure thickness at the crystal center and confirm it reads close to 13.1 mm. Oversized cases make the chronograph pushers sit high.
  3. Measure the lug width and confirm 20.0 mm. Then test that a standard 20 mm strap slides in without force.
  4. Set the dial under the loupe and check that the small seconds at 9 and the 30-minute counter at 12 sit on one horizontal line through the center.
  5. Read the brand text and the model printing at 6 o'clock under the loupe. Look for smeared edges, uneven spacing, and ink that sits above the dial surface.
  6. Check the date window at 3. Confirm the aperture is cut square, the date is centered, and the font matches the reference photo.
  7. Pull the crown to the setting position and move the hands. There should be no wobble in the hand stack and no slip in the stem.
  8. Start the chronograph and watch the central seconds hand sweep. Then stop it, reset it, and confirm the hand returns to 12 without drifting left or right.
  9. Time the 30-minute counter against a phone stopwatch over a full run. A counter that lags or jumps points to a worn movement.
  10. Inspect the crystal for sapphire thickness and blue-violet anti-reflective tint on both faces. Flat glass with no coating is a budget tell.
  11. Wind the watch fully, note the time, and let it sit until it stops. Compare the run to the power reserve the seller claims.
  12. Place the watch on a timegrapher in the dial-up position and record rate and beat error after five minutes of running.
  13. Flip the watch and read the caseback engraving. Letters should be cut clean, with no raised edges or shallow stamping.
  14. Shake the watch near your ear and listen to the rotor. A grinding or scraping sound means a dry or poorly seated bearing.
  15. Ask the seller for the exact movement name and whether parts are available. Quartz builds exist in this reference and are sold as automatic.
  16. Request a pressure test at 3 bar if you plan to wear it near water. If the seller cannot test it, keep the watch dry.
  17. Check the strap or bracelet for stitching density, grain, clasp engraving, and snug spring bars at both lugs.
  18. Photograph the dial, caseback, and clasp on arrival. This record supports a return claim inside the window.

Common Tells of a Low-Grade Copy

  • Subdials positioned off the center line.
  • Printed text that flakes or reflects under a loupe.
  • Pushers with long travel and a mushy reset.
  • Mineral glass with a green edge tint and no anti-reflective coating.
  • A caseback with laser-etched text instead of cut engraving.
  • Lume that dies within an hour and glows uneven on the hands.

Legal and Practical Notes

A first copy is not a genuine IWC watch. It carries no manufacturer warranty, no service support from the brand, and effectively no resale value. Counterfeit shipments can be seized at import and destroyed, and trafficking in counterfeit goods carries penalties under federal law. Treat the purchase as a wearable object, keep your expectations on the case and dial rather than on the movement, and buy only from a seller with a stated return policy.