Well, if you really want that on your phone you can get other calculator apps that are quite advanced. Might be easier than doing what you are doing.

Other calculator apps that might have different privacy policies, and who might call home to Google and Facebook despite reporting "no data collected", and which might disappear from the app store because it costs $100/year to have the privilege of providing a free app (e.g. as happened with OpenCalc. https://github.com/breeko/OpenCalc/issues/3 )

Believe me, I looked for a while. Nothing quite scratched the itch while also being free, ad-free, and private. I guess I sound quite picky, but SSH + python checks all the boxes.

You can use Siri Search on iOS as a calculator, which works the same way as Finder on a Mac — this keeps track of the entire expression when you’re doing it

> You can use Siri Search on iOS as a calculator

With the added benefit of having to press not just one, but two buttons in order to add a "+" sign. First press "123", then press "#+=" and now you can add your complex mathematical characters :)

I'm with you.

If I have to use the default keyboard to enter arithmetic expressions, I'd rather SSH to my own server. I'm not exactly sure of the privacy implications of typing things into Siri.

If you rely on a calculator then you owe it to yourself to check out pcalc. One of the few apps I maintain paying for these days.