I'd recommend looking at a cheap TI-36X Pro. It's solar powered and responsive. It's not a graphing calculator, but it has the nice graphing-calculator features most people really need (movable cursor and multi-line display with scrollable history).

It's not obvious from the page how much calculus it can do, and if it can solve algebraic equations. Or how much linear algebra it can do.

The manuals are online:

https://support.hp.com/us-en/product/hp-prime-graphing-calcu...

There is also an official emulator you can download for free which will give you some idea if you like it:

http://www.hp-prime.de/en/category/13-emulator

Thank you

So when I turn it on I will be able to start typing immediately without the delay of the TI-89? You've tried this calculator?

I hit the "ON" button and the screen lights up and it is responsive in less than 1s. I hit "ON" and immediately typed a number without waiting for it to light up and the number appeared exactly as I typed it.

I complain incessantly about devices that are laggy and I don't feel any lag with it.

Thank you. If you could compare it to the TI-89 lag I'd love to hear it. Regardless I really appreciate what you just took the time to write.