Quick answer
An IW329089 that is not genuine gives itself away at the case profile first. The real watch in this reference block is a 42 mm diver with a thick machined bezel and a case that stands a set height off the wrist. Copies shave the case down, thin the bezel, and print the dial text a fraction too large. Check thickness, bezel action, date window, and movement before you look at anything else.
What the IW329089 reference is
IW329089 sits in the IW3290xx block, which is the IWC Aquatimer Automatic line. Watches in this block share a 42 mm stainless steel case, an external rotating dive bezel, a screw-down crown, and a sapphire crystal. The calibre inside changes with the production year, so the block contains more than one movement. Because several dial and bezel variants carry numbers in this range, the first job in any authenticity check is to pin down the exact variant. IWC reference pages and the catalogue for the production year are the sources that count.
Checks that settle the question
- Measure the case with digital calipers. Record diameter across the bezel and thickness from caseback to crystal. Compare both figures to the published spec for the variant.
- Turn the bezel through a full rotation. Count the detents and note whether the grip feels machined or loose. A soft ratchet with uneven spacing points to a copy.
- Unscrew the crown and inspect the threads. The genuine crown seats flush against the case tube and turns with even resistance.
- Look at the date window. Check its distance from the crystal edge, the size of the aperture, and the font of the numerals.
- Read the dial text under a 10x loupe. Study the letter spacing, the thickness of each stroke, and the alignment of the printed marks.
- Inspect the lume plots. They should sit level in their recesses with a clean edge and no overspill onto the dial.
- Identify the calibre. Open the caseback or read the movement through a display back, then match the finishing and rotor engraving to the correct calibre for that year.
- Weigh the watch head on a kitchen scale. Record the number and compare it to a known genuine example of the same variant.
- Check the bracelet end links and clasp. End links should meet the case lugs with no visible gap, and the clasp should close with a firm click.
- Cross check the serial, the warranty card, and the asking price against the current market for the reference. A price far under market is the strongest single signal.
Red flags in listing photos
Seller photos hide a lot, but some faults survive compression. A bezel insert with a printed scale that fades toward the edges, a dial with a glossy finish under direct light, and hands with rough edges all point to a copy. Look for a caseback engraving that sits shallow in the metal, and for a crystal that shows heavy inner reflections because the anti reflective coating is missing on one side. Photos shot at an angle that hides the case flank are worth treating as a warning on their own.
Paperwork and serials
Genuine IWC paperwork carries a serial that matches the caseback and the movement. Check all three. A card with a mismatched number, a missing booklet, or a box that does not match the reference period tells you the package was assembled after the fact. Ask the seller for a photo of the caseback serial under bright light before you commit to anything.
Before you buy
Buy from a seller who accepts a return window long enough for an independent watchmaker to open the case. Have that watchmaker confirm the calibre, the case dimensions, and the dial print. If the seller refuses an inspection period, treat the refusal as your answer and walk away.