*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 S**max**:*

*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. *