The ZSCORETEST function detects outliers in a GTS by comparing the Z-score of its values with a given threshold.
The Z-score of a value represents the number of standard deviations (or median absolute deviations) it is away from the mean (or the median). If this value is greater than the given threshold, it is flagged as an outlier.
A LIST of ticks, corresponding to the outliers, is pushed back onto the stack.
This function only applies to GTS of type DOUBLE.