I did many sectors on the flight deck of BA Tridents in the 70's. 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. I have often wondered what made the chart move and how accurate it was and if it was based on a timer set to an estimated ground speed. Perhaps Blind Pew could enlighten me. I think the photo below shows the chart.
