During the evolution of Casio calculators there were many different types of display.
I will try to put a timeline in Casio's concept of the calculator display's.
(This will not include other brands displays and only what Casio used)

Illuminating pad (1954-1959)

The illuminating pad was used on the first prototypes, the 14-A and 14-B Casio calculators
To read a result is straithforward but not very useful for fast number reading.

When I type a simple calculation on a Casio 14-A and the product is 1,321,980.57
I will appear as follow on the Casio 14-A illuminating pad .

Another output result 31,943.8 looks as below.