Bob Gardner's book on RAF Clocks describes the history of these
here for details.
All RAF Sector Clocks are exceptionally rare.
Our recent research reveals that the ones made for Air Defence (the
command and control system of RAF Fighter Command) had inward pointing
segments. Most were electric slave clocks, and a few mechanical
ones were made. In the last fifteen years I have only seen two
examples. Clocks with outward pointing segments are almost all
mechanical clocks and were used in ops rooms throughout the RAF.
Let us know if you want to be added to our waiting
list for RAF Sector clocks.