Mathematical tables containing common logarithms (base-10) were extensively used in computations prior to the advent of computers and calculators, not only because logarithms convert problems of multiplication and division into much easier addition and subtraction problems, but for an additional property that is unique to base-10 and proves useful: Any positive number can be expressed as the product of a number from the interval and an integer power of This can be envisioned as shifting the decimal separator of the given number to the left yielding a positive, and to the right yielding a negative exponent of Only the logarithms of these "normalized" numbers (approximated by a certain number of digits), which are called mantissas, need to be tabulated in lists to a similar precision (a similar number of digits). These mantissas are all positive and enclosed in the interval . The common logarithm of any given positive number is then obtained by adding its mantissa to the common logarithm of the second factor. This logarithm is called the "characteristic" of the given number. Since the common logarithm of a power of is exactly the exponent, the characteristic is an integer number, which makes the common logarithm exceptionally useful in dealing with decimal numbers. For numbers less than the characteristic makes the resulting logarithm negative, as required. See common logarithm for details on the use of characteristics and mantissas.

অয়লার
Tables of logarithms
Early tables
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