The Harmonic Mean (H.M.) is a type of average used when values are defined in relation to some unit, like speed (distance/time), rates, or ratios. It is particularly useful when all data values contribute equally to a whole.
\[ H.M. = \frac{n}{\sum_{i=1}^{n} \frac{1}{x_i}} \quad \text{and} \quad \bar{x} \ (\text{A.M.}) \geq G.M. \geq H.M. \]