I have created a custom field on purchase line table - say U_TaxAmout . Now I want to calculate and update this field when Amount field is validated. However if I modify "Amount" field and use OnAfterValidate trigger, my user field does not get populated. But if I trigger on "Direct Unit Cost" or Quantity it works. Trying to understand why certain fields cannot be used to trigger inserting values to other fields. Does this mean Amount or Amount Including VAT fields do not have triggers?