Problem with Empty Number Field

I am in the middle of building an asp ms access application, one of the form pages is an update record form which updates several fields with the default values from the database displayed.  For my reports to work i need to have a value in all of the fields.  I have set the default value in access to 0 but if you delete one of the values in my update form and then submit the record is left with an empty value in the field. Any suggestions much appreciated.

many thanks in advance