Lago-Calculo-Sears - Francis WEB

Plasma, or Gas-discharge displays, were very popular in the late 70s or early 80s. They are mostly Orange. They were a transition between the early LED displays, and the later VFD or LCD.
The size was a little bit bigger than the LEDs, so they were primarily used in desktop models, such as the ones presented in this page.

I chose to have the 3 models above next to each other, to show that most of the calculators at that time were following the same design, with the numeric keys in the middle, the 4 operations on the right, and some additional function (memory) on the left.
There are many more examples of this technology, such as the Texas-Instruments Exactra 31 or the SCM (Smith Corona Marchant) 220 below: