That's not what I found online: the devices running customized SW were apparently used as personal calculators by the crew and they would have also used them for manual calculation in case their flight computer had a problem.

They weren't connected to other shuttle computers, were they?

I found multiple stories/blogs with recollections like this one from Smithsonian including the use of calculators on early missions before laptops were used:

https://airandspace.si.edu/collection-objects/calculator-han...

I remembered reading it in the newspapers at the time which would have probably make the reports generally pre internet (or pre newspapers on the internet) in the 1980's. Of course I could be remembering it wrong or it could have been a HP calculator ad.

Love to study those projects in more details - Not just the code, but also the design, testing, validation processes.