1. for n quantities ${\displaystyle x_1,x_2,\dots x_n}$, by the reciprocal of the mean value of their reciprocals:

   ${\displaystyle \frac{1}{X_{\text{h}}}=\frac{1}{n}\left(\frac{1}{x_1}+\frac{1}{x_2}+\mathrm{...}+\frac{1}{x_n}\right)}$ if none of the n quantities is equal to zero;

   ${\displaystyle X_{\text{h}}=0}$ if at least one quantity is equal to zero;

2. for a quantity x depending on a variable t, by the quantity $X_{\text{h}}$ defined by the reciprocal of the mean value of the reciprocal of the given quantity:

   ${\displaystyle \frac{1}{X_{\text{h}}}=\frac{1}{T}{\int }_0^T\frac{1}{x(t)}\text{d}t}$ if the value of the integral is finite;

   ${\displaystyle X_{\text{h}}=0}$ in other cases

Note 1 to entry: The harmonic 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 harmonic mean value of a quantity is denoted by adding the subscript h to the symbol of the quantity.