The buttons  [e] and [Ln] on the PentaCalc calculator compute exponentials and logarithms to base e (e is a transcendental number approximately equal to 2.71828182846). The buttons [10] and [Log] compute exponentials and logarithms to base 10. Hyperbolic functions are certain combinations of exponential functions, with properties similar to those of the trigonometric functions. They are useful for solving differential equations and evaluating integrals, and have other uses in mathematics and physics.