Casio FX-991EX is Casios most advanced scientific calculator with 552 math functions. Approved for major stage 3, 4, and 5 and recommended advanced GCSE, a/level or above Permitted by each UK test that can use calculators. As seen in large natural textbook display (Natural-V.P.A.M) textbooks, it has a mathematical expression, such as roots and fractions, increasing your understanding.