The Not valid tab of the Options form allows the user to specify the values of directions and data that must be filtered (i.e. excluded) from the analysis.
Both for directions and for data,
lower and upper thresholds can be indicated. Values smaller than the lower threshold or greater than the upper threshold will be excluded from the analysis.
Thresholds can be specified also for the third variable, when it is loaded within a MS Excel file.
The filtering options cannot be specified when data are loaded as frequencies.