This calculator is easy to use and it is for free. It has two different formats (scientific calculator and simple calculator) and you can switch between them with only one click.
The simple calculator has 28 keys with 7 main operations (addition, subtraction, multiplication, division, percentage, square root and multiplicative inverse).
The scientific calculator has 50 keys including all of the basic operations, trigonometric and hyperbolic functions, exponentiation, logarithm, factorial, etc. There are also two keys with constants preprogrammed (e and π).
The range of numbers that this app can manage goes from 4.9E-324 to 1.7976931348623157E308 (both in absolute value).
It is possible to select a different set of digits for the keyboard and/or for the screen (Western, Arabic, Persian, Chinese/Japanese, Devanagari (Hindi and others), Tamil, Bengali or Bangla, Telugu, Kannada and Malayalam)
Please, take into account that the app replaces the Western set (0123456789) by the new one, digit by digit. Not all of the available sets can be used on screen to write a number correctly. For instance, using the Japanese set, the number 100 will be displayed as 一〇〇, but the right codification is 百 (only one digit). The same problem could happen with other sets of digits.