Art wrote:
"The picture showed a seies of scan lnes across the screen at a slight
angle."

Yes. I think that is right but I learned about TV back in 1948 and
haven`t thought about it much since. As I recall, the designers of the
U.S. TV system decided to construct a picture consisting of two
interlaced fields. The first starts at the center of the screen at the
very top of the picture, sweeping to the right on a slight downward
slope, then retracing quickly to the lefthand edge of the picture. There
the next parallel but slightly lower line of field or frame starts being
written.

As I see it, the tilt or slope is strictly an arbitrary decision of the
designer but conformity is required of the standard to work within the
original system.

Best regards, Richard Harrison, KB5WZI