Thanks for your response Joe, that does work for the intended purpose but not quite what i originally wanted. I've edited my post to correct the wording.
In the future, it is probably best to just clarify it in a response, and not go back and change the original wording, as that pretty much can kill the flow of the thread and makes previous responses look out-of-place and confusing.
If you simply want to know for each record the percent that is complete, just add up your IIF statements and divide by 4, i.e.
Code:
Expr1: (IIf(IsNull([table1]![UniqueOrderNumber]),0,1)+IIf(IsNull([table1]![Colour]),0,1)+IIf(IsNull([table1]![PaperSize]),0,1)+IIf(IsNull([table1]![Cost]),0,1))/4
Note, you would NOT use SUM on this function. In Access, you only use SUM when aggregating multiple records, not multiple fields within a single record.