Filemaker does not have built-in conditional aggregate tools; either find the records in 2009 and use a summary field to average them, or use a relationship to filter the records and average the related values.
I'm not sure I follow... :( So is my calculation completely off?
So is my calculation completely off?
Yes. You cannot aggregate (sum, count, or average) records in the same table using a calculation field. Your test looks only at the date in the same record, and the expresion Average ( Audit_Total ) also refers to the local value only.