GrandTotal
The GrandTotal formula returns the grand total for the given aggregate formula. GrandTotal is shorthand for Subtotal(aggregate, "grand_total").
Syntax
GrandTotal(aggregate)
Function arguments:

aggregate (required)  The aggregate formula to use in the function.
 Examples:
Count(), Sum([Sales Amount])
 Examples:
Example
In a chart visualizing order counts per Product Type and Region, you can add a calculated column with the formula to the tooltip:
GrandTotal(CountDistinct([Product Type]))
To see an overall total count of distinct orders across all categories.

The calculation is shown in the tooltip in this example, but is usable anywhere an aggregate formula is allowed.