This photo, taken c.1946 in the Melbourne (Essendon) ACC, shows Control Officer Peter Allen making calculations on the ‘Rodoniscope’, a type of circular slide rule named after its inventor, Sydney Flight Checking Officer Norman Rodoni. The Rodoniscope was used to calculate the longitudinal separation of aircraft flying on the same air route. See below for a close-up view.

In the background Stan Sambell writes up the latest flight information on the Air Traffic Pattern Board.

The Rodoniscope and Air Traffic Pattern Board were replaced by flight progress strips and the flight progress board from 1948.

The original caption for this photo reads: "Australian regular internal air transport services carried 1,036,895 passengers and 18,472 tons of freight for the year 1947. Sixteen companies operate throughout Australia over a route mileage of 39,070 miles. When these figures were compiled Australia had the fine safety record of not having had a passenger fatality on any of its regular airlines for more than two years.

Behind this record of safety in civil Aviation is the story of the development of an aeradio service spreading over the length and breadth of the continent. Facilities operated by the Department of Civil Aviation include:- 57 Aeradio Communication Stations; 17 Radio Ranges [‘Lorenz’ beacons]; 51 radio beacons [NDBs and Markers]; 29 M/F D/F stations; 3 H/F D/F stations; five teletype stations; five flying boat bases.

Mascot (Sydney) and Essendon (Melbourne), Australia’s two biggest and busiest airports, each handle over 100 scheduled airliner movements each day besides hundreds of movements by light, non-radio-equipped aircraft."

Peter Allen later became Principal Training Officer at the DCA (ATC) Central Training College.