Short answer
IW371778 falls inside the IWC Portugieser Chronograph reference block, the IW3717xx range. IWC does not list every suffix variant in its public archive, so the exact case size, dial color and calibre for this number are not confirmed here. Treat any listing that states these details without a source as unverified.
Replica IW371778 Buying Guide: What to Check Before You Buy
A replica of this reference shows four tells: a base chronograph movement in place of the IWC calibre, numerals that are printed instead of applied, a caseback engraving with the wrong depth or font, and a serial number that does not match the paperwork.
IW371778 Replica Fake: What to Know Before Buying
Check the movement first
The Portugieser Chronograph line has used two calibres. Earlier 40.9 mm versions run calibre 79350, a modified Valjoux 7750 base. The current 41 mm version runs calibre 69355, an in-house movement with a column wheel. Ask the seller which calibre sits in the watch and ask for a photo of the rotor and the balance area.
On calibre 69355 the column wheel is visible through the caseback. On a clone you see a stock 7750 rotor with an engraved logo, or a decorated plate with no functional column wheel.
Case and dial checks
- Applied numerals: the Portugieser uses raised Arabic numerals. Replicas often print them flat.
- Subdial spacing: the two counters sit at 12 and 6 on the in-house version. A 7750 base forces a different layout.
- Caseback text: check letter height, spacing and the depth rating. Replica engraving is shallow and uneven.
- Crystal: sapphire with a double anti-reflective coat. A coated mineral glass shows a blue or purple cast under a lamp.
Papers, box and serial
Ask for the serial number on the caseback and the number on the warranty card. They should match. Ask for the dealer stamp and the date. IWC service records can confirm a watch was serviced, and a seller who refuses a service check is a risk.
Price as a signal
Secondary market asking prices for Portugieser Chronograph references sit in the low to mid four figures in US dollars, depending on age and condition. A price far below that range points to a replica or a watch with a replacement movement.
Questions to ask a first copy seller
- Which movement is inside, and can you show the rotor?
- What is the case diameter and thickness in millimeters?
- Are the numerals applied or printed?
- Does the watch come with a box, card and matching serial?
If a seller cannot answer the first three, stop. The answers cost nothing and take one photo each.