The logarithm to base a(>0) of a positive number b is denoted by logab=x, where ax=b. Logarithms have the fundamental property loga (bc)=logab+logac. A logarithm to base 10 is usually denoted by log and a natural logarithm, i.e. a logarithm to base e, by ln. Before the advent of computers and calculators, logarithms were used in evaluating products.