Hello,
The ratio of the Baird system was 3:7 with 30 lines. But the real ratio was 1:2; wich is a bit wider.
In order to make it happen, 3 lines on each side were wider than the lines composing the main section of the picture.
Wich leaves us with 24 lines of normal width and 6 larger lines.
If one normal line is 1 pixel wide, how wide are the 6 larger lines ?