In 1966 there were ads for desktop electronic calculators (see
links below). They were costly, about $1,600 to $2,000.
As shown in the ads, consumers still had a choice among
various classic electro-mechanical models. Despite being
clunky and slow, the old models were still very popular
until the early 1970s, when electronics finally won out.
I can't believe how expensive they were, and don't forget,
$2,000 back then is like $10,000 today. It would seem a
few circuit cards would be enough to do basic calculations
and display the results on a screen. Unlike a computer, they
didn't need a high pulse rate and could use cheaper slow
transistors.
Friden
https://archive.org/details/Nations-Business-1966-04/page/n66
Marchant
https://archive.org/details/Nations-Business-1966-05/page/n17
Victor (appears to be chip based)
https://archive.org/details/Nations-Business-1965-11/page/n121
also, Friden tape word processor
https://archive.org/details/Nations-Business-1965-11/page/n21