Short answer
No single feature proves an IW323736 is real. Work through four checks in order: the caseback engraving against the official reference data, the movement and its finishing, the dial and date printing under magnification, and the measured case dimensions. A real watch passes all four. A counterfeit fails at least one, and usually two.
Before you start
- A 10x jeweler's loupe
- Digital calipers readable to 0.01 mm
- A scale readable to 1 gram
- The official IWC specification sheet for reference IW323736
- A watchmaker who will open the caseback and photograph the movement
Authentication procedure
- Read the reference and serial off the caseback and confirm the reference string matches the IWC format used for the IW3237 family, where the trailing digits code the case, dial, and strap combination.
- Place the watch head on the scale and record the weight in grams.
- Measure the case diameter and thickness with calipers across the 9 and 3 o'clock axis.
- Compare the weight and the two measurements against the published specification for IW323736.
- Study the caseback engraving through the loupe and check engraving depth, edge sharpness, and letter spacing.
- Examine the crown and confirm it is signed, seats on clean threads, and screws down without grit or wobble.
- Inspect the dial under the loupe and check applied index alignment, lume fill, and the crispness of the brand and reference text.
- Look at the date window and compare the numeral font and the centering of the disc against the dial aperture.
- Ask the watchmaker to open the caseback and read the calibre number stamped on the movement bridge.
- Photograph the movement and check the finishing: Geneva stripes on the bridges, circular graining on the plates, polished bevels, and a signed rotor.
- Inspect the strap or bracelet and the clasp, and confirm the buckle carries the correct signature and the stitching or end links match the reference.
- Match the serial on the caseback to the serial on any warranty card, and confirm the card and box belong to the same reference.
- Take the watch to an IWC authorized service center and request a written authentication opinion.
Where counterfeits fail most
- Caseback engraving that is shallow, laser-soft, or set in the wrong font.
- A movement that is a generic ébauche with a decorated rotor rather than the calibre the reference calls for.
- Case thickness that runs a fraction of a millimeter off spec because the case was cast, not machined.
- A date font that is too wide or too bold for the aperture.
- Unsigned or wrongly signed clasps and buckles.
Bottom line
Weight, measured dimensions, and movement finishing are the hardest details for a counterfeiter to copy at cost. If the seller refuses to let a watchmaker open the caseback, treat that as a failed check and stop there.