A fake IW371655 fails at least one of four checks: the reference engraving, the caseback text, the movement behind the sapphire back, and the dial print. No counterfeit uses an IWC calibre. Start there.
What IW371655 should be
IWC uses the 3716xx block for the Portugieser Chronograph. The current 41 mm generation measures 41 mm across and runs on calibre 69355, an in-house automatic chronograph. IWC lists a rate of 4 Hz and a power reserve of 46 hours.
The suffix matters. IW371655 is one variant among many in the same block, and dial color, case metal, and strap change with the suffix. IWC's own reference list is the source for the exact build of IW371655. Check that list before you judge a watch.
Check 1: Reference engraving
Genuine: the reference sits between the lugs, laser etched, even depth, clean font. Copy: shallow marks, off-center placement, wrong spacing between digits. Compare the digits with the number printed in the listing.
Check 2: Caseback
A display back shows the movement. The rotor carries the IWC name and the calibre number. Genuine engraving is crisp with filled text. Copies show flat stamping, blurred edges, or the wrong calibre number for the reference.
Check 3: Movement
Look for an IWC signed oscillating weight and finish on the bridges. Replica movements show generic bridges, rough edges, and copied rotor text. A watchmaker can open the case and read the calibre. That step costs little and settles the question.
Check 4: Dial and hands
Two subdials sit at 12 and 6. The IWC and SCHAFFHAUSEN print is sharp under a loupe. Indices are applied metal. Copies show soft print, loose indices, and subdials that sit off-center.
Price, papers, warranty
A genuine steel Portugieser Chronograph sells used in the thousands of US dollars. Offers far below that band are a warning. IWC lists an extended warranty when the owner registers the watch on the brand site, so a seller with an active registration has a record you can check.
Short checklist
- Match the reference engraving to the listing.
- Read the calibre number on the rotor.
- Look at the dial print under a loupe.
- Compare the asking price with market listings.
- Ask a watchmaker to open the case.