How add a custom function to SummaryType

[rh_it]

Hello everybody, unfortunately the SummaryType doesn't allows to easily add a customized function because displays only:

1.jpg

But I noticed that to add a custom function to SummaryType you need to duplicate the column
1.5.jpg

Then in the duplicated column try to add "SummaryType" a press Add
2.jpg

In this manner you will able to add a custom function to your column!
3.jpg