HP calculators were great. I’ve owned several of the postfix based ones. (I.e. one enters 12, 30, + instead of 12 + 30)

The article may not make it clear how many efforts were going on in that timeframe to manufacture calculators. The first electronic calculator I saw at MIT was a desktop system by Wang; it had a Nixie tube display, see [1,2,3].

The first handheld calculator I ever came into contact with was in 1971 when I saw a student with a Bowmar Brain.

[1] https://peoplaid.com/2020/08/12/the-story-of-an-wang-develop...

[2] https://en.m.wikipedia.org/wiki/Wang_Laboratories

[3] https://en.m.wikipedia.org/wiki/Nixie_tube

[4] http://www.vintagecalculators.com/html/bowmar_calculators.ht...