The fx-991es plus 2 is a scientific calculator ideal for secondary school and university degrees with natural ‘natural textbook display' to display formulas and results exactly as in textbooks. Equipped with 417 functions, including: Equation resolution, calculation of synthesis values and variability indexes, matrix and vector calculation, regression and correlation coefficients, complex numbers, calc key (temporary memory formula), 40 physical constants, integral and differential calculus Combined power supply: Solar and alkaline button cell LR-44.