Rolex has had an enormous set of inventions and enhancements developed for their timepieces over the years.  In 1972 Rolex developed the hack.

The issue that early Rolex calibers would lose seconds when pulling out the crown and setting the time (hour and minutes hands).  With hacking technology, the seconds hand can be stopped and adjusted and synched to another source.  This feature increases accuracy.  Since the seconds don't stop in non-hacking timepieces, you could never get an exact synchronized time with any resource.  The closest you could get would be to the minute.

There are many instances when having hacking and to the second accuracy is essential.  Military operations is clearly the most obvious.  Hacking was not uncommon in some timepieces during the war to coordinate bombing runs, but it wasn't until 1972 when Rolex adopted the technique.



With the release of the caliber 1570 in 1972, it was now possible to stop the sweeping seconds hand by pulling out the watch crown, activating a hacking lever that interrupted the balance wheel and simplifying the act of setting the watch accurately.

The enhancement is a small channel machined into the caliber plate.  It is fitted with a spring tension which is activated straight through to a thin metal bar located between the winding pinion and  touching the balance wheel.  It works similar to a hand break on a car so as you pull out the crown the seconds movement can stop and be adjusted precisely.