The CITICAL CT‑991MS is a non-programmable, dual‑power scientific calculator with a two‑line, 10+2 digit LCD display. It competes closely with well-known models like Casio’s fx‑991MS and fx‑991ES. Here’s a detailed overview:

? Key Features & Functions

• Dual Power Supply: Solar cell + button battery — reliable both indoors and outdoors.

• Display: Two-line, showing both entry and result simultaneously (10-digit mantissa + 2-digit exponent).

• Number of Functions: Around 401 scientific functions, including:

  • Basic arithmetic & fraction conversion.

  • Trigonometric and inverse trig functions.

  • Hyperbolic functions.

  • Logarithmic and exponential calculation, including natural logs and base‑10 logs.

  • Factorials, permutations, combinations.

  • Integration and differentiation.

  • Matrix and vector operations.

  • Complex number arithmetic.

  • Base‑n conversions.

  • Statistics: standard deviation, regression, summation.

  • Equation solver, random number generator, multi-statement replay features.