A common logarithm is a logarithm which uses as its base. For example is equal to because is equal to
Log base-10 can be written but since it is used so often, it has been shortened to Most calculators use this base when you press the button. For positive numbers of , the definition of base-10 logarithm is as follows:
The numbers and can be written as powers of 10. In other words, and . If you calculate base-10 logarithms from these examples, you will see that they indicate the exponents of the powers of ten.
You can also calculate common logarithms on a calculator.