I have found an interesting info here:
https://dragonden.agiledragongroup.com/c/resources/issue-with-calculated-averages-in-summary
It talks about the well-known issues with averages at the Summary level in reports. Specifically, it says:
Birst has an account level setting called ‘LegacySummary Flag’.
Only Infor can turn this on by submitting a support ticket. Once enabled, the summary operation ‘expression’ works to perform the calculation at the summary level.
I'd like to have a detailed explanation on what such Flag does. In particular, does it impact both Visualizer and Designer?
(Side comment: in Visualizer, in CrossTab it is possible to use “Expression” as a Custom Summary. In Tabular format, “it is not supported”. Why?)