How can I calculate the difference between the initial value of a field and the updated value on update on a form? I have an actual hours field for a unique technical support case record. When a user updates the value of actual hours I want to calculate the difference between the original value and write one record to a case hours history table with the after update value for actual hours and the date time of the update. I have the update writing the record to the history table but I'm having problems using the fields' BeforeUpdate, OnDirty, Or AfterUpdateEvents to calculate the difference between the initial value and after update value and writing to the history table. Alternatively, once many records are written to the history table for one record how can a report be written to calculate any differences in actual hour values from week to week between the history records?