Question: For how long did the Working Lunch producer alternate different broadcasting systems?

full_context: Document 1: Business Tonight: Business Tonight is a business news talk show on CNBC until c. October 1997. The show was hosted by Sue Herera.
Document 2: World Business Report: World Business Report is a television business news programme produced by BBC News and shown on BBC World News and the BBC News channel on weekdays. There are two editions broadcast each weekday, at 0745 and 1130 GMT. Each edition lasts 15 minutes. The main presenters of the programme are Tanya Beckett, Sally Bundock, Sally Eden, Juliette Foster, Alice Baxter, Aaron Heslehurst, Jamie Robertson and Philip Hampsheir. Sara Coburn, Maryam Moshiri and Nancy Kacungira act as relief presenters. It was first broadcast in 1995.
Document 3: Asia Business Report: Asia Business Report is a business news programme produced by the BBC and is shown on BBC World News during the Asian morning hours. This programme used to be available exclusively in Asia-Pacific, South Asia and Middle East but, as of a 1 February 2010 revamp, is aired worldwide. It is also currently aired on the UK's domestic BBC News and BBC One channel three times daily in the early hours of the morning as part of the "Newsday" programme.
Document 4: Working Lunch: Working Lunch is a television programme broadcast on BBC Two which covers business, personal finance and consumer news, broadcast between 1994 and 2010. The programme was first aired on 19 September 1994. It had a quirky, relaxed style, especially when compared to other BBC business shows such as "World Business Report". In April 2010, the BBC announced that the programme was being cancelled at the end of July 2010. "GMT" with George Alagiah took its place in the schedule at 12:30 on BBC Two.
Document 5: Usapang Business: Usapang Business is the business television show created by ABS-CBN News and Current Affairs and aired on ABS-CBN and ABS-CBN News Channel, the format of the weekly news magazine program that aired Tuesday nights after "The World Tonight" features innovative businesses that are on the fast-track in the Philippines. This is aired from 1996 to 2002.
Document 6: Today's Business: Today's Business is an American business news television program that aired on CNBC in the early morning, 5–7 am ET timeslot, hosted for the end of its run by Liz Claman and Bob Sellers. It was replaced by "Wake Up Call" on Feb 4, 2002. The show covered news that was expect to affect the stock market trading day ahead.
Document 7: 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 8: 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 9: CNBC Tonight: CNBC Tonight is a weeknight business news programme broadcast live from 1800 - 2000 HK/SG/TWN time on CNBC Asia from 16 February 2005 to 16 December 2005. It took the timeslot vacated by 3 former CNBC Asia programmes, "Business Center", "The Asian Wall Street Journal" and "e". The two-hour programme combined the mix of Asian and global news headlines, corporate news and personal finance. It also featured upscale lifestyle features on travel, health, food and leisure. CNBC Tonight was co-hosted by May Lee and Teymoor Nabili.
Document 10: 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 11: 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 12: 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 13: 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 14: 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 15: 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.
ground_truth: six months
sub_queries: Who is Working Lunch by? Answer: BBC
For how long did the BBC alternate different broadcasting systems? Answer: six months