Oh, another favorite feature:  The card had a signal
line that could activate
 the degaussing circuit on the bundled AT&T monitor.  I almost fell out of my
 chair when I ran diagnostic software that printed something like
 "Degaussing..." and then was quickly followed by a loud noise and the familiar
 "twisty pix" distortion of a monitor in its degaussing cycle...  scared the
 crap out of me. 
I beleive the HP9845C (colour monitor) had a DEGAUSS command in the BASIC
that would energise the degausing coil. And a CONVERGE command that would
display the appropriate patterns for doing convergeance adjustments. Alas
I only have a 9845B (with the enhanced mono monitor) so I cna't try them out.
-tony