Logarithms I — O/L Mathematics

Some numbers in the real world grow by multiplying, not by adding — the strength of an earthquake on the Richter scale, the loudness of sound in decibels, the acidity of a solution as a pH value, the money in a compound-interest account. To measure and compare things that grow this fast, we need a tool that answers the question "what power produced this number?". That tool is the logarithm, and this lesson is where you meet it for the first time.