Rule 3021. Form of affidavit of verification. The affidavit of verification must be to the effect that the pleading is true to the knowledge of the deponent, except as to the matters therein stated to be alleged on information and belief, and that as to those matters he believes it to be true. If it is made by a person other than the party, he must set forth in the affidavit the grounds of his belief as to all matters not stated upon his knowledge and the reason why it is not made by the party.