Question: For how long did Waldo Maguire's employer alternate different broadcasting systems?

full_context: Document 1: BBC Television: Mechanically scanned, 30-line television broadcasts by John Logie Baird began in 1929, using the BBC transmitter in London, and by 1930 a regular schedule of programmes was transmitted from the BBC antenna in Brookmans Park. Television production was switched from Baird's company to what is now known as BBC One on 2 August 1932, and continued until September 1935. Regularly scheduled electronically scanned television began from Alexandra Palace in London on 2 November 1936, to just a few hundred viewers in the immediate area. The first programme broadcast – and thus the first ever, on a dedicated TV channel – was "Opening of the BBC Television Service" at 15:00. The first major outside broadcast was the coronation of King George VI and Queen Elizabeth in May 1937. The service was reaching an estimated 25,000–40,000 homes before the outbreak of World War II which caused the service to be suspended in September 1939. The VHF broadcasts would have provided an ideal radio beacon for German bombers homing in on London, and the engineers and technicians of the service would be needed for the war effort, in particular the radar programme.
Document 2: BBC Television: Baird Television Ltd. made Britain's first television broadcast, on 30 September 1929 from its studio in Long Acre, London, via the BBC's London transmitter, using the electromechanical system pioneered by John Logie Baird. This system used a vertically-scanned image of 30 lines – just enough resolution for a close-up of one person, and with a bandwidth low enough to use existing radio transmitters. Simultaneous transmission of sound and picture was achieved on 30 March 1930, by using the BBC's new twin transmitter at Brookmans Park. By late 1930, 30 minutes of morning programmes were broadcast Monday to Friday, and 30 minutes at midnight on Tuesdays and Fridays, after BBC radio went off the air. Baird broadcasts via the BBC continued until June 1932.
Document 3: High-definition television: Colour broadcasts started at similarly higher resolutions, first with the US NTSC color system in 1953, which was compatible with the earlier monochrome systems and therefore had the same 525 lines of resolution. European standards did not follow until the 1960s, when the PAL and SECAM color systems were added to the monochrome 625 line broadcasts.
Document 4: BBC: The British Broadcasting Corporation came into existence on 1 January 1927, and Reith -- newly knighted -- was appointed its first Director General. To represent its purpose and (stated) values, the new corporation adopted the coat of arms, including the motto ``Nation shall speak peace unto Nation ''.
Document 5: BBC Television: After a series of test transmissions and special broadcasts that began in August 1936, the BBC Television Service officially launched on 2 November 1936 from a converted wing of Alexandra Palace in London. ``Ally Pally ''housed two studios, various scenery stores, make - up areas, dressing rooms, offices, and the transmitter itself, which then broadcast on the VHF band. BBC television initially used two systems on alternate weeks: the 240 - line Baird intermediate film system and the 405 - line Marconi - EMI system. The use of both formats made the BBC's service the world's first regular high - definition television service; it broadcast from Monday to Saturday between 15: 00 and 16: 00, and 21: 00 and 22: 00. The first programme broadcast -- and thus the first ever, on a dedicated TV channel -- was`` Opening of the BBC Television Service'' at 15: 00. The first major outside broadcast was the coronation of King George VI and Queen Elizabeth in May 1937.
Document 6: High-definition television: Since the formal adoption of digital video broadcasting's (DVB) widescreen HDTV transmission modes in the early 2000s; the 525-line NTSC (and PAL-M) systems, as well as the European 625-line PAL and SECAM systems, are now regarded as standard definition television systems.
Document 7: Color television: After a series of hearings beginning in September 1949, the FCC found the RCA and CTI systems fraught with technical problems, inaccurate color reproduction, and expensive equipment, and so formally approved the CBS system as the U.S. color broadcasting standard on October 11, 1950. An unsuccessful lawsuit by RCA delayed the first commercial network broadcast in color until June 25, 1951, when a musical variety special titled simply Premiere was shown over a network of five East Coast CBS affiliates. Viewing was again restricted: the program could not be seen on black - and - white sets, and Variety estimated that only thirty prototype color receivers were available in the New York area. Regular color broadcasts began that same week with the daytime series The World Is Yours and Modern Homemakers.
Document 8: Ronald Mason (drama): Ronald Mason (8 September 1926 – 16 January 1997) was a director and producer of drama for the BBC, a BBC executive in his native Northern Ireland at the height of the Troubles, the Head of BBC Radio Drama as successor to Martin Esslin and was active in the European Broadcasting Union (EBU).
Document 9: BBC Television: As a division within the BBC, Television was formerly known as BBC Vision for a few years in the early 21st century, until its name reverted to Television in 2013. It is responsible for the commissioning, producing, scheduling and broadcasting of all programming on the BBC's television channels, and is led by Danny Cohen.
Document 10: BBC Television: After a series of test transmissions and special broadcasts that began in August, regular BBC television broadcasts officially resumed on 1 October 1936, from a converted wing of Alexandra Palace in London, which housed two studios, various scenery stores, make-up areas, dressing rooms, offices, and the transmitter itself, now broadcasting on the VHF band. BBC television initially used two systems, on alternate weeks: the 240-line Baird intermediate film system and the 405-line Marconi-EMI system, each making the BBC the world's first regular high-definition television service, broadcasting Monday to Saturday from 15:00 to 16:00 and 21:00 to 22:00.
Document 11: Waldo Maguire: Waldo Maguire (31 May 1920 – 23 November 2005) was a British broadcaster for the BBC. He had a long career with the BBC, culminating in his appointment in 1966 as the Controller of BBC Northern Ireland. He served in this position until 1972.
Document 12: British Railways Board: The British Railways Board (BRB) was a nationalised industry in the United Kingdom that operated from 1963 to 2001. Until 1997 it was responsible for most railway services in Great Britain, trading under the brand name British Railways and, from 1965, British Rail. It did not operate railways in Northern Ireland, where railways were the responsibility of the Government of Northern Ireland.
Document 13: BBC Television: The two systems were to run on a trial basis for six months; early television sets supported both resolutions. However, the Baird system, which used a mechanical camera for filmed programming and Farnsworth image dissector cameras for live programming, proved too cumbersome and visually inferior, and ended with closedown (at 22:00) on Saturday 13 February 1937.
Document 14: World in Action: Some of the most prominent figures in 20th-century British broadcasting helped to create "World in Action", in particular Tim Hewat, "the maverick genius of Granada's current affairs in its formative years", and David Plowright: but also Jeremy Isaacs, Michael Parkinson, John Birt and Gus Macdonald and its most long-serving executive-producer, Ray Fitzwalter. The series developed the skills of generations of journalists and, in particular, film-makers. Michael Apted worked on the original "Seven Up!". Paul Greengrass, who spent 10 years on "World in Action", told the BBC: "My first dream was to work on "World In Action", to be honest. It was that wonderful eclectic mixture of filmmaking and reportage. That was my training ground. It showed me the world and made me see many things." He later told "The Guardian": "If there's a thread running through my career it's "World in Action" – the phrase as well as the programme."
Document 15: Robert McGladdery: Robert Andrew McGladdery (18 October 1935 -- 20 December 1961) was the last person to be executed in Northern Ireland.
ground_truth: six months
sub_queries: What is Waldo Maguire's place of employment? Answer: BBC
For how long did the BBC alternate different broadcasting systems? Answer: six months