At one time there were at least four B&W video transmission standards in Europe (we
had a tube TV with a
4-position selection knob to support them). 625/50 regular, 625/50 inverted in some way
(?) used by the Dutch
speaking Belgian stations, 819/50 for France, and a different 819/50 for French speaking
Belgian stations.
Not part of the _video_ signal, but part of the overall signal : IIRC continental Europe
(mostly?) put the sound
carrier 5.5 MHz way from the video carrier, but the UK had a 6MHz offset.
-tony