Something I
forgot to note was that this instrument (the 4261A) was
actually manufactured for HP by Yokogawa, I'm not too sure where the
HP part ends and the Yokogawa begins, maybe it was designed by HP and
built by Yokogawa, or maybe the whole thing was a contracted design
for HP by Yokogawa.
Yokogawa is not on the list of HP acquisitions.
Well, hardly an acquisition if they (partially) owned it from the start.
http://www.hpmuseum.net/divisions.php?did=39
YEW is still around today, my dad has purchased scopes for the lab at work
from them. YHP is separate from YEW, I guess.