You can look up the logarithmic function table or use a calculator. Lg represents a logarithmic function with the base of 10, such as lg 10= 1, lg 100=2. If lgx = a, then x = 10 a, then if you want a, you need to know how many times x is 10. In mathematics, log is used to represent general logarithm, and any number can be used as the base.