# Limitations of calculations in dimensional reporting

Minimal checking exists for calculations. If your calculation uses an invalid expression, your report results may contain unexpected values.

In addition, you should define member summaries as follows:

` ``summary_function` (`currentMeasure` `within set`

`set_reference`)

where `set_reference` is a level or set inserted from the Source tab .

Unless otherwise required, `summary_function` should
be the aggregate function. If you use an explicit summary function,
you may encounter problems with measures (such as profit margin, distinct
count, and so on) that have complex rollup values, and/or scenario
or account dimension members that do not roll up.

Know your data, and confirm with the owner of the cube where overriding the automatic aggregation is safe.

Because of these limitations, summaries of calculations may not provide reliable values. For convenience, you may have to build reports where row summaries and calculated member columns intersect. In such reports, these intersections may contain unexpected values. In contrast, row calculations intersecting with column aggregates using the aggregate function are safe because the calculation is performed on the reliably summarized values.

## Units of Measure

When creating calculations, you may encounter problems with the units of measure. For example, the calculation Cost * Cost returns the unit of measure * (asterisk) instead of a currency unit of measure. To avoid this problem, change the format of the corresponding column to obtain the desired unit of measure.

## Limitation When Using Dimensional Functions with Running and Moving Summaries

IBM
Cognos Analytics does not currently support queries that contain both
dimensional functions and running summaries or moving summaries. For
example, when you drill down in a report, the query uses the dimensional
function `children`

, which is not compatible with running
and moving summaries. Running and moving summaries are supported for
only the overall level of a dimension.