Calculates the population variance of all values in the SourceChart over the time period, using the n method (biased): TotalVariance / n.
Chart to calculate the maximum from
Lower bounds index into the SourceChart
Upper bounds index into the SourceChart
TimeStamp of the new value
Note that this function is a class procedure so it may be called even if the TRSCustomChartFunction is not instantiated.
The function can also be called by custom functions. For example, you could create a custom function that calls this function and then does something with the result