Very good calculator 1 1

This calculation is in line with Casio Graph robust, easy enough to use, with many functions and programmable relatively easily. Your old programs can be copied without problems, they will walk. Whatever use you are going to make the rather large screen and with a good definition should make this easier. Power is supplied by batteries quite common (you can even use rechargeable batteries).
For me the really important point is the robustness (I have very bad memories of that view, other brands).
The fact that we can download programs, with an active community, the Internet is also a significant advantage.