Firstly, NEVER do calculated fields at the Table level! This violates rules of normalization and is not compatible with any other database program!
I do not know why Microsoft decided to allow this feature in newer versions of Access. It is a bad idea.
On top of that, it is very limited in the kinds of calculations you can do.
And I do not think you can do dependent calculations as default values in table anyway.
In Access, all calculations should be done at the query level. Queries can be used for just about anything that Tables can, so there really is no reason to want to do them at the Table level instead of the Query level.
The calculated field in your query would look like:
Code:
PaymentCode: IIf([CostCentre]="example1" Or [CostCentre]="example2",123,890)
So note that "PaymentCode" would NOT be in your table. It is a calculatd field in your query.