The need for engineering calculator begin to experience when you go to high school.
On the lessons of physics, and some astronomy, we have to calculate that it is impossible on a conventional calculator — sine, cosine, and tangents of different angles, arccosine, arctinus, integrals and so on.
Sometimes it is necessary to calculate roots of two, large fraction, that takes a lot of time. Not everywhere allowed to use the telephone at the lesson for the calculations — this calculator is a huge advantage.
It can solve equations, simplify expressions with complex numbers, working with matrices (almost all, it functions because 417) — mathematics, he also useful.
It is useful in many physical contests where a phone is not exactly to use it.
It comes in a box, inside of which lies a detailed instructions on using all features.
Unfortunately, Citizen 991ES batteries not included — but they are not necessary, can be charged by light bulbs. He does not waste a lot of energy, and for several months they didn’t have to change.
991ES calculator is not very expensive — in the region of 500 rubles. In the shops of SPB can be found at a price two times higher, but I didn’t notice the difference in quality. Works quickly, properly, what more do you need?
The thing came in 3 weeks — the usual time, not very often they come faster. Box was a little dented, but it’s not very scary.