Tagging the primary statements - Step 4 - Calculations
The fourth step in tagging a primary statement is to set the mathematical relationship of the tags that were used in each report section.
When validated (Step 5), Report Authority will test the calculations as defined using the values in the report. Calculations are set using the Calculation Hierarchy panel on the right-hand side:
Relationships are created by:
- Dragging an element and dropping it onto another element
- Changing its weight to be either 1) Add, 2) Subtract, or 3) Do Not Rollup.
See this video for a worked example with explanations:
Limitations to the calculation hierarchies that can be created
The XBRL calculation (linkbase) specification is limited in terms of the types of calculations that can be created. It can create simple rollups containing different primary tags in the same periods. It is not capable of the following calculations:
- Calculations spanning different periods, such as Closing = Opening + Movements
- Calculations containing the same element but different secondary tags (dimension members), for example Equity (Total) = Equity (Issued capital) + Equity (share premium) + Equity (etc)
For this reason, the only calculations that typically need to be created in the Statement of changes in equity are for subtotals within the movement of equity - such as the calculation of "Total comprehensive income".
Please note the XBRL specification contains other mechanisms for creating validations that may test for the limitations mentioned above. You may therefore have to resolve some of these issues but you are unable to create such validations in your extended taxonomy.
Elements without any children
Sometimes an element is used which does not participate in a calculation hierarchy that is possibe to be created. In. this case, it will exist as a root node without any children. Report Authority will ignore any of these elements when creating the extended taxonomy so can be ignored:
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