I recently asked a software recommendation question for a TI-83 series emulator and TI-Basic interpreter. Are questions about calculator hardware, software, and programming languages on-topic for Retrocomputing?
I would say most definitely, if the calculator has a microprocessor in it. The early days of home and small business computing included calculators, many of which were home-built kits like the Science of Cambridge Mk14.
Programming, and maintenance of systems like the HP calculators with little magnetic cards for the programs would definitely come under the scope of computing. Also, questions about Reverse Polish Notation.
The TI range falls well within this ambit.
Whether mechanical calculators are on topic would, I think, be a separate question.
Yes - but only if they're not still in production. The Z80-based TIs are still commercially available. The defining consensus in What constitutes “retro”? was that the device or technology had to be off the market.
So Saturn-based HP calculators would be on-topic, but newer ARM-based ones would not be.