Hi everyone!
I've heard a lot of people talking about hack features but I've never actually known what it it,any answers would be appreciated .
Thanking you in advance
Francesco

Francesco,
The hack feature stops the second hand. I believe it originated for military watches to allow syncronizing watches.

Evan

it's the ability to stop the seconds hand in order to sync the watch with other watch once the stem is pull out .

When you pull up on the stem to set the watch, a small wire is engaged and pushed into the balance wheel to stop it from moving.

Here's the wire in "brake released" mode on a 4992B:

I had the same question but then I seen this youtude video of the hack in action

http://www.youtube.com/watch?v=Aly1D3bhXV0