The logarithmic function is very specific function used widely in various fields. Generally, we do not know the true value of the logarithm. So we use an approximation with some digit. Most of mathematical textbooks provide a table of common logarithm with proportional parts or not. So we can find an approximate value of the real number without a calculator. The value of proportional parts in several tables of common logarithm was found different. According to the analysis of various types, we propose how to correct use of the proportional parts in the table of common logarithm.

logarithmic function, common logarithm, proportional parts.