Originally Posted by
suninmyeyes
I seem to remember on some there was a chart at the front on a roller that was clearly mechanically operated as every now and again there would be a judder and it would spasmodically move. I do not believe the movement was caused by the flight crew.
If you think about it, the map is only capable of displaying a given bit of airspace at any point in time.
If the aircraft's position moves off the top or bottom of the map, the map just scrolls a bit.
But if the position moves off the side of the map, the map needs to fast-forward (or back) to find the relevant swathe.
Older PPRuNe thread on the Trident moving map here:
Moving maps displays - ancient mechanical!