Special variables can be use with the expressions.
<!--T:59--> @count - Total number of lines returned in a table.
<!--T:60--> @row - current line number.
<!--T:61--> @sum[Column] - Sum of indicated column.
<!--T:6263--> @avg[Column] - Avg of indicated column like @sum[Column] / @count
<!--T:64-->
@prev[column] - Previous row column value
@prev[column] <!- Previous row column value -T:65--> @accumCol[column] - Current accumulated column value. Useful to calculate Variable Avg ("@accumCol[column]" / "@row")
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