The VFD was introduced at the 1967 Society for Information Display
(SID) symposium by Tung-Sol (Wagner Electric).
I imagine it was a single bottle (digit) like the digivac DT-1704. I have some as GE Y-1938. pics:
Dieter's Nixie WorldThere is an aggressive sea of patents on VFD's. Futaba seems to have been first to make them small.
"... VFD's in multi-digit form ... they are only made in Japan"
source 1973In the 1970's, display technology competition was fierce. I think the VFD lost out for some reason due to no real manufacturing base in the USA or patents.
One problem is vacuum fluorescent displays needs more power, at least 1W (filaments) including the DC-DC converter.
So they were not so great for battery-powered devices.
But it is strange there were many pocket calculators using VFD displays, although an AC adapter was the norm with them.
I've never seen or recall VFD's being used in any portable/handheld test equipment. Just calculators.
Of the portable multimeters that emit photons as I call it, I only know of the Sinclair PDM35 handheld 3-1/2 digit used LED bubble displays.