A log table, or logarithm table, is a reference chart containing pre-calculated logarithms of numbers. Its primary purpose is to simplify complex arithmetic calculations involving multiplication, division, exponents, and roots by converting them into simpler operations of addition, subtraction, multiplication, and division, respectively. Most standard log tables use base 10 (common logarithm).

A log table and an antilog table perform opposite functions. A log table is used to find the logarithm of a number (e.g., finding the value of log₁₀(100), which is 2). In contrast, an antilog table is used to find the original number whose logarithm is known (e.g., finding the antilog of 2, which is 100).

To find the log of a number, you first separate it into its characteristic and mantissa. For example, to find log(234.5):Step 1: Find the Characteristic. The number has 3 digits before the decimal, so the characteristic is (3 - 1) = 2.Step 2: Find the Mantissa. Look for the row '23' in the log table. Move across this row to the column '4'. Note this value. Then, in the same row, find the value in the 'mean difference' column for '5'. Add the mean difference value to the main value.Step 3: Combine. The final log value is the characteristic plus the mantissa.