One of my sources of money is tutoring students in maths and physics. The reason is my undergraduate training in physics: the math and physics we learn is good for teaching high school (grades 11 and 12) maths and physics.
I've noticed is how clumsy students are when it comes to using their scientific calculators. I've seen this in both high school and university classes. The worst case I've seen was a student with a very powerful scientific calculator, and the method of use is to write intermediate steps on paper, when it could all be done using the calculator itself with the suitable use of the ANS key and the memory.
Since I couldn't let that go, I would nag about reading the manual. Sometimes, I would use trail and error to figure out how their calculator works, and then teach them how to use it so that they wouldn't waste time during exams.
I've recently been tutoring a grade 11 student who's in the International Baccalaureate programme. Since the programme places such a large emphasis on the end exams (it reminds me of the Cambridge Tripos system), and because graphing calculators are allowed (even encouraged), I've asked myself if I should buy a TI-84+ calculator so that I could assist students who use such calculators.
Fortunately, the google play store came to the rescue. I was able to find an emulator (Andie Graph) for the TI-83+ (which has almost exactly the same functions as the 84+) which also doubles as an emulator for the models TI-82,83,85, and 86 models. The emulator serves as the virtual machine within Android, and within that virtual machine, it runs the roms of the various TI models. Roms, by the way, are the operating systems of the calculators. A screenshot of the emulator is on the side.
Good thing I searched. I've looked at the price of the TI-84+ and I was staggered at the PhP 8.5 K price. I will buy one if I ever have to teach in an IB school, but for now, a Chinese Android tablet worth PhP 2.9 K running the emulator is good enough. Paradoxically, the cheaper tablet is actually more powerful than the calculator. However, if you do need to take the AP, SAT, or IB exams (or even university level exams in introductory physics), only the real calculators are allowed.