The PDP-6 display had a 1024×1024 point raster, randomly addressable at 30 μs a pop. To gain insight into integer lattice reduction, Rich had me display all 2^20 points, sorted by fractional part of x π + y e, with a ~30 second period. The appearance was a nonrectangular creeping grid. But depending on ambient lighting, visual acuity, and caffeine consumption, different viewers saw different grids. You could find fast grids by guessing a velocity vector and sweeping your finger thusly across the screen. If there was such a grid, your brain could lock onto it. To hide a picture or message, slightly perturb the temporal order of those points you want to stand out. Only viewers skilled at seeing rapid grids will notice. --rwg It should also be possible to Morse-code messages by rapidly blinking LED auto taillights to leave dotted and dashed afterstreaks, if you know how to look. On 2018-04-09 16:49, Bernie Cosell wrote:

On 9 Apr 2018 at 15:46, Mike Beeler wrote:

...

... Nowadays, even if the PC were easily available, instruction rate is way too fast for a CRT to keep up with, but perhaps a pseudo-random sampling would accomplish the same effect. However, it wasn’t helpful enough to be a great tool, IMHO.

Got me wondering. I worked with BBN's PDP-1d, which was a very tricked-out PDP-1 (it had two drums, 9-channel mag tape drives, the prototype of the PDP-6 memory bank machinery). All of that stuff had lights on almost every register. The 'lights bank' was the width of the PDP-1 console and went to the ceiling, packed with lights all the way (Mike might have see that system.. I don't think any of you had). I got very good at understanding what was going on in the timesharing system just by a glance at the lights. Mike got me wondering what that lights display would be like with modern components. The displays on the two drums would be unreadable -- all the lights on, but at varying brightnesses. Same with the main CPU registers and everything else. But then, beyond that, I got to wondering if a suitable savant could still do what I did but by understanding the brightness patterns as they flowed back and forth

/B\

Bernie Cosell bernie@fantasyfarm.com -- Too many people; too few sheep --