What is the meaning of Logarithmic scale?

On a' Logarithmic scale' or graph, comparable percentage changes in the value of an investment, an index, or an average appear similar even though the underlying change in value may be significantly different. For example, a stock whose price increases during the year from $25 a share to $50 a share has the same percentage change as a stock whose price increases from $100 a share to $200 a share despite the fact that the dollar value of the second stock is four times the value of the first. Similarly, the percentage change in the Dow Jones Industrial Average (DJIA) as it rose from 1, 000 to 2, 000 is comparable to the percentage change when it moved from 4, 000 to 8, 000.