Use of the harmonic mean: On averaging count-rate data for variable-time, fixed-count intervals

The average of count rates from measurements performed by accumulating a fixed total number of counts over a variable time interval should be obtained with harmonic mean. Use of an arithmetic mean in these cases will give intuitively incorrect results. Uncertainty estimators for this harmonically averaged counting rate, such as the standard deviation, must also be suitably transformed to correspond to that for the harmonic mean