I found an unusual handhel pocket terminal.
It's housing is the same as the older LED pocket calculators used by Texas
but is is not the TM990/xxx terminal as used for Texas own PLC's or TMS9900 based
I've seen a number of similar units and I was told these were indeed
handheld terminals for the older network equipment. I have one that
sounds just like yours that was made by Gould, and just picked up one
made by Codex that is similar.