also known as "decimal logarithm". the base 10 logarithm is 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 "leading number" of the logarithm, and the positive pure decimal (or zero) is called the logarithm. the "mantissa" of a number. commonly used logarithms can be found in logarithm tables.

express a positive number in scientific notation as the product of a decimal containing one integer 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