Short answer
A fake Calibre 4206 is a movement stamped or sold as a 4206 that never left the original maker's factory. In practice these are Asian automatic calibres, often clones of a common Swiss three-hand design, dressed up with an engraved rotor, painted screws, and a stamped bridge plate. The case, dial, and hands may be genuine parts pulled from a real watch. The engine inside is not. A genuine 4206 leaves the factory with a documented jewel count, a stated beat rate, and a parts chain that a watchmaker can service. A counterfeit has none of those three things.
Checks you can run before you open anything
Write down the watch reference number. Look up the caliber figure the maker publishes for that reference. If the seller cannot name the caliber, or names a number that does not appear in the maker's own documentation, stop there. Ask for a photo of the movement through the display back. A seller who refuses that request has answered your question.
Step-by-step verification
- Record the case reference and the caliber number the maker lists for it.
- Photograph the movement through the display back at 10x with a loupe or macro lens.
- Compare the rotor engraving against a known genuine photo: font, cut depth, letter spacing, and the placement of the caliber number.
- Count the jewels and compare the total against the figure in the maker's service manual.
- Place the watch on a timegrapher and read the rate, amplitude, and beat error in six positions.
- Confirm the beat rate matches the published spec, for instance 28,800 vibrations per hour for a 4 Hz caliber.
- Wind the crown through twenty turns and note the resistance and the sound of the ratchet.
- Pull the crown to the setting position and check that the seconds hand hacks.
- Advance the date through midnight and watch for a clean, single jump.
- Leave the watch off the wrist and time how long it runs before it stops.
- Hand the watch to a watchmaker with a genuine parts account and request a written opinion.
Red flags on the movement itself
- Rotor text that looks printed or laser burned rather than cut with a visible groove.
- Screws painted blue instead of heat blued, so the slot edges show bare steel.
- Circular graining that runs across the jewel settings instead of around them.
- A jewel count that sits above or below the maker's spec.
- Bridge edges that are sharp and unfinished where a genuine caliber shows anglage.
- Rate readings that drift past 20 seconds per day between positions.
- A caliber stamp cut in a different typeface from the caseback hallmarks.
When to walk away
Any one red flag can be explained. Three together cannot. If the jeweling is wrong, the engraving is soft, and the timegrapher shows a wide spread, the movement is not a 4206 no matter what the rotor says. Counterfeit watches move through the same channels as other counterfeit goods, and customs agencies seize them in volume every year. Pay for an independent appraisal before you pay for the watch, and keep the written report.