The power to which a number, called the base, has to be raised to give another number. Any number y can be written in the form y=xn. n is then the logarithm to the base x of y, i.e. n=logxy. If the base is 10, the logarithms are called common logarithms. Natural (or Napierian) logarithms (named after John Napier; 1550–1617) are to the base e=2.718 28…, written logey or lny. Logarithms were formerly used to facilitate calculations, before the advent of electronic calculators.
A logarithm contains two parts, an integer and a decimal. The integer is called the characteristic, and the decimal is called the mantissa. For example, the logarithm to the base 10 of 210 is 2.3222, where 2 is the characteristic and 0.3222 is the mantissa.