Using Code Editor to create Level of Detail calculated field (PU_SUM?) Merged

(Disclaimer: More of a question than a idea! - also posted in the ARIS Community)

I'm trying to work out a way of using the Code Editor (or any other calculated field method) to generate a fixed Level of Detail (LOD) value for an imported dataset. Specifically, I'd like to create a field with the total activity/case duration for all records - i.e. not at the individual case level.

So, for example, the fixed LOD value for the dataset below would be 7 days:

Not sure how to accomplish this? I think that the PU_SUM function *might* possibly be the way ahead, but a) I can't seem to find an example of how to populate the syntax requirements correctly (i.e. PU_SUM(scope: Table, source: Table, field: Field | Calculation, filter?: Boolean)) and b) I suspect that this would only roll up to the case level, which is already available from the standard Case Duration measure.

One of the reasons that I would like the ability to create fixed Level of Detail calculations of this ilk is to be able to generate an Index to compare distribution and performance metrics - for example, in the App Builder, I can configure the Number of Occurrences and Activity Cycle Time measures to display as a percentage share within the App, but I can't seem to build calculated fields for the same percentage share values to then compare and Index the distribution metric (i.e. Percentage Share of Count of Number of Occurrences (Base (100%) value = (CT (Number of Occurrences)) with the performance metric (i.e. (i.e. Percentage Share of Sum of Activity Duration (Base (100%) value = (SUM (Activity Duration)).