Usually floating point arithmetic is available to use if desired, because the arithmetic is done by most computer hardware very quickly. The down-side of floating point arithmetic is that it is not always exact, and is mostly useless for rocket science, because of only 14 decimal digits of accuracy (with double precision floats), and because of a growing round-off error with each calculation, sometimes even less digits are accurate. Rational number arithmetic is exact if all numbers are rational. Interval arithmetic can be used to easily calculate the total possible error of an inexact arithmetic system. Complex number arithmetic is generally supported by allowing the imaginary unit (formula_1) in expressions and following all of its algebraic rules.