Need your advice for a visually impaired person

[Accutron]

If VFDs are okay, the options are virtually limitless as long as you only need standard adding machine functions. VFDs are multispectral with a large blue component however, which is probably not so good for geriatric macular degeneration. Color sensitivity degradation is most severe on the blue end of things. Something with an orange Panaplex gas discharge display is probably going to be the best intersection of price, availability, digit size and visibility, but it would require getting a pre-1975 machine.

The Olympia CPD 512 looks like it has a gallium phosphide green LED display.