Early French `HD' Television.

[tubesrule]

The number of lines in a standard needs to be mutliples of small integer numbers. This was required by early sync generators since small integer dividers were the easiest to create using blocking oscilators. This web site has lots of technical information on many different video and RF standards, and shows the integer dividers for most standards.

http://www.pembers.freeserve.co.uk/W...Standards.html