[Dottore]

There are some very good fakes out there.

In almost all cases the giveaway is if the second hand doesn't sweep.

But I have occasionally seen a fake where the second hand does sweep.

The other way to tell pretty easily is by weight and heft. Many fakes are far too light.

Also, look closely at the printed words on the dial. Particularly the small wording "superlative chronometer officially certified". Almost all fakes do this very badly.