April to September 2006 to allow major upgrade work on the tunnels and rolling stock. The line's limited access meant that this was the first time that the units had been brought above ground since their introduction 12 years earlier. The refurbishment of the trains saw them painted in the London Underground white, red and blue livery in place of the Network SouthEast colours used since the stock's introduction. Operation The 1992 Stock features both automatic train operation (ATO) and automatic train protection (ATP) which effectively allow the trains to drive themselves. The ATO is responsible for operating the train whilst the ATP detects electronic codes in the track and feeds them to the cab, displaying the target speed limits. This functionality is configured via a master switch in the driver's cab which can be set to one of three positions: Automatic, Coded Manual and Restricted Manual. In Automatic mode the ATO and ATP are both fully operational. The driver is only required to open and close the doors and press a pair of "Start" buttons when the train is ready to depart. The driver is then tasked with overseeing the operation of the system and can intervene at any time. The ATO controls the train to the desired target speed, whilst the ATP is ready to apply the emergency brakes if the Maximum Safe Speed is exceeded. However, it is not communications-based train control found on the other lines. In Coded Manual mode, the ATO is disabled and the driver operates the train manually, however, the ATP is still detecting the codes in the track and restricting the driver's actions. The speedometer on 1992 stock is of the horizontal strip design showing two speeds: the Current Speed in green, indicating the speed at which the train is actually travelling, and the Target Speed indicating the speed at which the train should be travelling. Although the target speed is always active whilst running in Automatic or Coded Manual mode, in the latter mode a change in the target speed is indicated with an upwards or downwards tone depending on whether the target speed is increasing or decreasing. Should the driver exceed the target speed, an alarm sounds and the emergency brakes are automatically applied until the train is below the target speed; the alarm then stops, for example if the target speed is 30 mph and the driver is going