Major Error on Calculator involving Series

[retoa]

I am also in some trouble with the Prime at school.
I had to choose between Prime, Texas and Casio for my students, I choosed the Prime because I find it better to use as nspire-cas and class-pad.

Now I am working with my students with complex numbers and it turns out that in home the Prime does not give the correct answer if you calculate the square root of a complex number when both the real and imaginary part are negatives.
This is quite bad, because if the students calculate it they will find a wrong result.
The fact that the Prime can not compute Riemann Zeta function for complex values is not so bad, you do not receive an answer, no problem.
The problem in when you do a calculation and the calculator gives you a wrong answer.

I am a former electronic engineer and I wrote a lot of software for complex telecommunication devices, so i know very good what it means to write, debug and release a software. I am not criticizing the work done by HP, I know they did a great job.

But still I can not give my students a calculator which gives wrong answers, they use it in the tests we do in the classroom and they will go at the exams with it...

So now I have to decide if next year I can still propose the HP Prime to the new students or if I have to change it. I still find the Prime a very good calculator, I like it and I will continue to use it, but the students are still learning math so they need a calculator that always gives correct answers.

I will decide in august what I will do...

Thank you to all for the work done !!!