Media armonica

The harmonic mean is one of the three Pythagorean means. It is calculated by taking the reciprocal of the arithmetic mean of reciprocals. 

The harmonic mean is used to calculate the average of ratios or rates,  such as speed of a vehicle, or in business to find out the price-to-earnings ratio of a company. 

Consider a car moving from point A to B with a speed of 30 miles per hour. Then to point C with 70 miles per hour and finally return to point A with 80 miles per hour.

The arithmetic mean of the speed in the above journey is 60 miles per hour, which is skewed towards the larger values. In contrast, the harmonic mean avoids this bias in data by giving more weight to the smaller values. 

Begin by taking the reciprocal of the given values. Then calculate their arithmetic mean. Finally, take the reciprocal of this arithmetic mean to get the harmonic mean.

Note that the harmonic mean should not be used if any of the data values is zero.