Being an engineering student, I needed a calculator. I bought the 991W two years back only because I wanted a calculator with dual power. But over a period of time I realized the power of the 991W.
The two line view helps you to view both your calculation and your answer. The dual power keeps you worry free about the battery running out when you need it most.
Though ofcourse the many features, does make you need to read the manual before you know all of them. The manual wasn’t very great and comprehensive.
The best for both a novice and an expert.