Also known as "decimal logarithm". Logarithms with base 10 are represented by the symbol "lg". For example, lgA represents the logarithm of A with base 10, where A is a real number. The common logarithm of any positive number can be expressed as the sum of an integer and a positive pure decimal (or zero); the integer part is called the "head" of the logarithm, and the positive pure decimal (or zero) is called the "mantissa" of the logarithm. Common logarithms can be found in logarithm tables.

Express a positive number in scientific notation as the product of a decimal containing one digit and an integer power of 10 and then take the common logarithm

For example: lg200=lg(10^2*2)=lg10^2+lg2=2+0.3010

lg20=lg(10^1*2)=lg10^1+lg2=1+0.3010