Statistical Moments
The RTD curve is described by its statistical moments  of which
the centroid of distribution     and spread of distribution     are
the most important numerical values.

Sample throughput and sample dispersion are related to     .
The throughput is limited to maximum sampling rate Smax:

The     value can be expressed either in time units or in volume units, for constant  flow rate  system.  For systems based on programmable flow, such as SI only volume based     can be used for system evaluation. A useful property of statistical moments is their additives:

In this way the  contribution  of a  component on dispersion
can be evaluated from the change of overall variance, by
changing one component volume or geometry, while keeping
other variables unchanged.