The Label on Charts field allows you to define the label that will appear for a given column on a chart or graph. This is only applicable when viewing your report as a chart or graph.
If this label is not defined, then Prospero will use the first header row defined on the column and if there is no label to use from there, then will default to using the column number as the label.
You may use any standard Header variables in this label field. However, the Header selection screen (as is used in the Header fields) is not available to allow you to construct label values using that Header Definition selection dialog.