A logarithm consists of two parts called the characteristic and the mantissa . The characteristic of the logarithm is that part preceding the decimal point and the mantissa is that part of the logarithm which follows the decimal point. Decimal numbers expressed in scientific notation have, or upon proper shifting of the decimal point can have, values ranging only between zero and one multiplied by an integer exponent of ten. This integer is the characteristic of the logarithm of the number, which can then easily be obtained by inspection. Since mantissas are irrational endless numbers, a useful table can only list them to a reasonable number of places.
Tables are commonly available giving values to two, three, four, five and six places.
Electronic calculators can be used to obtain values to more places. A two-place table of common logarithms is given in the Table above. Interpolation between table entries can be used if desired. This table, like most tables of common logarithms, leaves the characteristic to be determined by inspection. It may be used to obtain either logarithms or antilogarithms.