Short answer
A fake IWC Portugieser ref. IW371446 fails at least one measurement. The genuine watch has a 40.9 mm steel case that is 12.3 mm thick and runs IWC caliber 79350. Copies run thicker, use a stock Valjoux 7750 or an Asian copy of it, and print the dial text in the wrong font. Check thickness and the caseback first.
The genuine reference IW371446
IWC Schaffhausen built the ref. IW371446 in the Portugieser Chronograph line. Listed specs:
- Case: stainless steel, 40.9 mm diameter, 12.3 mm thick
- Water resistance: 3 bar
- Movement: IWC caliber 79350, automatic, 28,800 vph, 44-hour power reserve
- Base movement: Valjoux 7750, reworked by IWC
- Crystal: sapphire front, sapphire display back
- Subdials: 30-minute counter at 12 o'clock, small seconds at 6 o'clock
- Date: window at 3 o'clock
- Strap: alligator leather, steel folding clasp
- Dial: blue, applied numerals, leaf hands, no luminous paint
Six checks
1. Case thickness
Use a caliper. Genuine: 12.3 mm. Known copies: 13.5 mm to 14.5 mm. The extra height holds a thicker movement and a spacer ring. Look through the display back for a plastic or metal spacer around the movement.
2. Subdial layout
The genuine has two subdials. The 30-minute counter sits at 12. Small seconds sit at 6. There is no 12-hour counter. Copies built on a stock 7750 shift the subdial centers and leave the hands sunk in the recess or sitting above the rim. The date sits at 3 on both, but the genuine date font is thin and the aperture edge is sharp.
3. Movement
Caliber 79350 shows a decorated rotor with the IWC Probus Scafusia medallion in gold. Bridges carry Geneva stripes. Screws sit flush. Copies show a stamped rotor, laser etching in place of a medallion, and tool marks on the bridges.
4. Dial print
The IWC logo and the word SCHAFFHAUSEN are applied with tight letter spacing and even stroke weight. Copies show letters that touch, a heavy stroke, or a raised logo with soft edges. Compare the numeral shapes: the 4 is open on the genuine, closed on many copies.
5. Caseback engraving
The reference number IW371446 and a serial number are engraved, not printed. Edges are crisp. Copies show shallow, wide engraving or a laser mark with a dark fill. Match the reference number to the case and the papers.
6. Crystal and coating
IWC fits sapphire with antireflective coating on both faces. The blue dial reads near black at some angles and deep blue at others. Single-sided coating gives a blue or purple flare under a lamp.
What a photo cannot show
A photo cannot show case thickness, rotor finish, or how the chronograph pushers feel. Genuine pushers take a firm push and snap back. Copies feel soft and gritty. Weight also separates the two: the genuine head weighs about 80 g on a steel clasp strap. Numbers vary with strap size.
Buying checks
- Ask for a side photo of the case on a flat surface with a caliper in frame.
- Ask for a caseback photo with the movement running.
- Check the serial number against an IWC service record.
- Pay a watchmaker who has handled the reference to authenticate the watch in hand.
Unknown: IWC does not publish a full list of copy serial numbers, so serial checks alone do not prove a watch is genuine.