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Authentication
Verify the IWC-signed rotor and IWC movement finishing through the caseback; a generic ETA 7750 without IWC decoration indicates a movement swap.
- Cal. 79320 is an IWC-modified Valjoux 7750; the movement must show IWC decoration and signing to confirm authenticity.
- The cam-operated chronograph architecture (not column-wheel) is normal for this caliber.
| Area | What to check | What is correct | Red flag |
|---|---|---|---|
| caseback | IWC-signed rotor and Cal. 79320 movement finishing | IWC-signed rotor visible through caseback; IWC movement finishing and decoration on bridges; Cal. 79320 identity confirmed | Generic ETA 7750 without IWC signing or decoration; unsigned rotor; no IWC-specific finishing |
| dial | Portofino dress chronograph dial layout | Clean dress-oriented dial with 3-register chronograph layout; Portofino case proportions appropriate for this movement | Dial layout inconsistent with Portofino specifications; any non-standard sub-register configuration |
| case | Portofino round case with pushers | Clean round Portofino case; both chronograph pushers operating cleanly with no binding | Either pusher binding or sticking; case shape inconsistent with Portofino line |
- Original IWC Portofino strap; factory replacements are standard.
Authentication guide
The IW391036 is a 42mm Portofino Chronograph with a Cal. 89361 (in-house flyback chronograph). The Portofino family targets the dress watch segment; thin case, slim lugs, and a silver or white dial are the identifying characteristics. The flyback complication distinguishes this from the standard push-button chronograph found in many competitors.




