Definitions of hacking / non-hacking movement:
A hacking movement is one that stops
the second hand when you pull the crown to the time-setting position,
so you can set it to the second. A non-hacking movement doesn't do this.
Hack or Hacking: Describes the feature of a movement whereby the seconds hand can be stopped for exact setting of the time. Originally a military term for this feature.
Here's the first and most important caveat: The watch must not be fully wound. If you just wore it while playing tennis, cricket, or chopping a cord of wood...set it aside and wait 20 hours.
1. unscrew the stem to the time setting position.
2. apply a very slight reverse torque to the winding stem, not so much that the minute hand flys back, but just enough to make the minute hand move ever so slightly in reverse.
3. maintain this pressure for 10-15 seconds, do not let up.
4. the watch will stop.
Other layman instruction:
If you pull out the crown to the time setting position and then very slowly turn the hands anti-clockwise whilst putting a little back pressure on the crown, you can stop the second hand until it synchronises with your time source. Iit gets easier with practice.