Hey Daniel,
you won't be able to use this variable for further processing. because this gets calculated when the data is retrieved from the database. It's only available for display in a datagrid.
If you'd want to use it in a chart you can retrieve and aggregate the data yourself in a new attribute (or object) at time of creating the graph. Or you can check for a solution where you always pre-process the data whenever a decimal value gets changed.
Hi Daniel,
Larn is right. You can not do it with the aggregation on the datagrid. But you can try the solution in this thread: https://forum.mendix.com/link/questions/96068