> My understanding was that it was the phosphor, but I could be wrong. I
> recall someone (Iwatsu, perhaps) came up with some sort of hybrid. It had a
> tube that worked like an analog scope but they could read the grid/phosphor
> back. That was digitised with slower A/D's and then put back up on the
> screen.

I have seen such a beast.  It was an analog storage tube with screen dump
capability.  The act of printing would clear the display, however; if memory
serves, a bright green line would sweep from left to right, wiping the dis-
play.  I think what was happening is that the unit was sensing how many
electrons/photons/whatever got knocked off as it did the bright green scan.

If memory serves, the printout was that sort of icky stuff that a lot of
microform printers use; I would not be at all surprised if the device had
a 1D scanning tube and photo-imaged the data it was reading off the main
view screen as the paper rolled through.

The thing that still amazes me, though--all that old technology with tubes,
mercury delay lines, punched cards, etc. actually WORKED.  Nowadays it would
probably be unthinkable to build such things with the quality required for
good operation but back then that's what people had to work with.

Amazing how times change.