The sacramentary assumes the presence of a choir, deacon and subdeacon. At the time that these books were written it was not yet the custom for the celebrant to repeat at the altar whatever was sung by the ministers or the choir, as became the rule in the Tridentine Mass. Thus Sacramentaries contain none of those parts of the Mass such as Scripture readings, Introits, Graduals, Offertories and so on, and only included the prayers specific to the celebrant such as the Collects, Prefaces, and Canon.