Multiplication becomes addition after you take logs. That makes many things easier to understand and manipulate. Exponential trends become linear. The geometr

Multiplication becomes addition after you take logs. That makes many things easier to understand and manipulate. Exponential trends become linear. The geometric random walk where you multiply by X or divide by Y with equal probability becomes an additive random walk where you add log(X) or substract log(Y) and you can represent that as a standard random walk (where the up and down steps have the same magnitude and probability) plus a trend.