I found this guy used on shopgoodwill.com for about $20 USD a few months ago. It was on my list of calculators to procure, but the going rate of $130 USD for a new one was way out of my range. I was ecstatic to find one in such great shape for a low price!
This is an amazing calculator with some glaring issues that make it more of a mixed bag than it could have been.
This is the last calculator produced by TI with the OS that was originally designed for the TI-92, TI's first calculator with a built-in CAS. The fact that it was written for a device with a full QWERTY keyboard is glaringly obvious. The UI has been crammed into a standard graphing calculator form factor in such a way that some key combinations can't be silk-screened on the keypad. Base 10 log is Green Diamond + 7, for example.
The other huge problem with it is the speed reflects when it was designed. This calculator was released in 2004, and has had no upgrades since. As such, it is ungodly slow to perform a lot of calculations. In most cases, it performs on par with the Casio fx-991EX, a calculator which costs 1/7 as much. Graphing speed is pretty close to the Casio CFX-9850G from the mid 90s. This thing is unbelievably slow compared to most currently available calculators.
On the other hand, with the software being as mature as it is, it is amazing. There are program packages for the TI-89 Titanium that have no rival on any other platform. EEPro and MEPro are both freely downloadable from TI and provide a suite of activities, functions, and references customized for electrical engineering and mechanical engineering, respectively.
I'm very happy with this machine, and it does get quite a bit of use in spite of its shortcomings.
I've only ever needed to use higher level math in school as well, but I am very happy that I know how to do it.
I've forgotten all that stuff now, it's been 8 years of not using any of it. Calc 1 & 2 along with DE were fairly straight forward for me and I was able to do so of the easy stuff in my head, but I hit my limit HARD with PDE and complex analyses. Now, I doubt I could do anything harder then find the derivate of X^n lol
I try to keep my skills sharp, but I know that there are things that I've forgotten over the years, too.