Ok I see what you are trying to do. So you won't be able to overwrite the natural aggregation from base Accounts to a parent Account. The value at the parent Account is dynamically generated from the aggregation of the base members and is not stored. We should be careful changing the base level data or adding additional data records to the data unit to resolve this situation ( can effect overall performance and consolidation times ). I'm guessing those are Flow members in columns and the member "Error" is a member in the Flow Dimension? Then Error is being populated from the Closing Flow member? So is the Flow member "Error" using a stored calc or a dynamic calc? Anyways, you won't be able to use Math.Abs within the api.Data.Calculate. You could also use Math.Abs inside of Confirmation Rules if you choose to make this a Confirmation Rule to support this process as well.
