Eavesdropping on a printer's signature

[nobody@soda.berkeley.edu]

While doing a summer (1980?) co-op with Raytheon Submarine Signal
division in Newport RI, a milk-truck-sized van pulled up out front
and opened a sliding side door.  Inside was a line printer
that was busy printing out the same text that an internal (in the
middle of the building, perhaps 150 feet away) line-printer was
printing.   There were mistakes, but it was readable.

My guess is that with all the electromechanical pulses the printer
was emanating this was pretty easy.  Probably harder to do with a
laser printer...