This photo gallery explains the order of how it used to happen. At about 5 minutes to1pm the ball was lifted to the middle (to alert ships that the signal would be due shortly), and then at 2 minutes to 1, ascended further up the pole to the top. The ball was then dropped at 1pm by an electrical signal sent directly from Greenwich. The time was recorded when the ball began to drop, not when it reached the bottom of the pole. Today the mechanism operates automatically every hour between 9am and 5pm for public entertainment only.
When the Trust took over the running of the Tower, the ball mechanism was controlled by a pneumatic system that had become very unreliable. It failed completely in front of a crowd of about 200 people at the midnight drop scheduled for New Year's Eve 2003. The pneumatic mechanism has since been completely replaced by Gillett and Johnston with a new mechanism operated by an electric motor and large toothed-belt. The motor is computer controlled and synchronised to the Rugby atomic clock signal - so we are confident its accurate.
Although most of the original mechanical & electrical mechanism is present, it is not used in order to avoid wear and damage.