The TI-59 ... ahh, THAT was a calculator! I used one in my college years. Still have it. Although I use a Windows-based TI-59 emulator when I need a quick calculation or two.
Later on I bought a TI-99/4A and I was hooked. I LOVED that thing. Still have a number of them gathering dust in the garage.
One comment though: The TI-99/4A was one of only two REAL COMPUTERS to be released in the 1970's-1980's microcomputer boom. If you learned to program it in Assembly, as I did, it had a "floating workspace" which coexisted in the single linear memory space, which along with programs and data, also used memory locations for I/O. All addressed in the same manner as linear memory. This architecture is "classic" computer architecture. Only Texas Instruments and DEC released microcomputers like this.
All other micros used microprocessors, which have to move data from linear memory, to on-board registers, and then back out. This ham-strings their operation and makes them much, much slower. That was why the TI-99/4A ran acceptably fast enough, even with a horrendously slow clock rate. Of course, the sheer speed of microprocessors was so blindingly fast by the mid-1980's that it didn't matter about all the time needed to swap data in and out of on-board registers. Current speeds are so fast that nobody cares.
But "back in the day" it sure was nice to see that the TI-99/4A was using assembly language statements that could have come straight from mainframe computers. When the IBM PC first came out in 1981, a game released with it was Adventure. If memory serves me, way deep in the Wizard's cave are copies of LWPI magazine. That instruction, Load Workspace Pointer Immediate, is used in linear memory addressing. I could use it in TI-99/4A assembly. It DOES NOT exist in a microcontroller-based assembly language such as had to be used on the 8088-based IBM PC. That was proof to me that the Adventure game had been ported from a mainframe implementation.