There are two main reasons to use logarithmic scales in charts and graphs. The first is to respond to skewness towards large values; i.e., cases in which one or a few points are much larger than the bulk of the data. The second is to show percent change or multiplicative factors.

What is the purpose of using logs?

Logarithms are a convenient way to express large numbers. (The base-10 logarithm of a number is roughly the number of digits in that number, for example.) Slide rules work because adding and subtracting logarithms is equivalent to multiplication and division.

What does log mean in statistics?

A logarithm is an exponent. The logarithm of a number to the base b is the power to which b must be raised to produce produce the number. Thus, suppose y = b^x.