If I recall corectly the very first ( early 1970's )Cessna 800 series FD had two orange balls at the end of the gull wing. You were suposed to line up the balls with a corresponding moving dot on the side of the display. I may have the details a bit wrong as it has been a long time since I have seen one. In any case it could not have been very popular as cessna went to a conventional 2 cue display for the 800( B ) system introduced in 1975.