1. for n positive quantities $x_1,x_2,\dots x_n$, by the positive nth root of their product:

   ${\displaystyle X_{\text{g}}={(x_1\cdot x_2\cdot \mathrm{...}\cdot x_n)}^{1/n}}$

2. for a quantity x depending on a variable t, by the quantity $X_{\text{g}}$ calculated from the values of the quantity x(t) by the expression

   ${\displaystyle \log \frac{X_{\text{g}}}{x_{\text{ref}}}=\frac{1}{T}{\int }_0^T\log \frac{x(t)}{x_{\text{ref}}}\text{d}t}$

   where $x_{\text{ref}}$ is a reference value

Note 1 to entry: The geometric mean value of a periodic quantity is usually taken over an integration interval the range of which is the period multiplied by a natural number.

Note 2 to entry: The geometric mean value of a quantity is denoted by adding the subscript g to the symbol of the quantity.