Baird Television Ltd. made Britain's first television broadcast, on <answer>30</answer> 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 <answer>30</answer> 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 <answer>30</answer> March 19<answer>30</answer>, by using the BBC's new twin transmitter at Brookmans Park. By late 19<answer>30</answer>, <answer>30</answer> minutes of morning programmes were broadcast Monday to Friday, and <answer>30</answer> minutes at midnight on Tuesdays and Fridays, after BBC radio went off the air. Baird broadcasts via the BBC continued until June 1932.
How many lines made up the picture on Britain's earliest TV broadcasts?
30