It is to be noted
that the feasts are classified as Great, Medium, and Lesser.
The Great Feasts are those of the Lord, those of the Theotokos, two of the Forerunner (his Nativity and his Beheading), and that of the Foremost Apostles Peter and Paul. They are indicated by the circled cross (I in this Service Book). These feasts have a Vigil, and the whole service is for the feast according to the rule.
The Medium Feasts of the Saints have two signs, the first a cross and halfmoon (II in this Service Book). On these festivals, the Vigil is celebrated, and at Matins a Canon of the Theotokos is included according to the rule. The second is a cross only (III in this Service Book). On these feasts, the Vigil is not celebrated. At Vespers, Blessed is the man . . . the first antiphon, and at Lord, I have called . . . stichera on 6 (and if you will on 8) 3 readings, and its own aposticha. At Matins, Polyeleon and Gospel, Canon on 8, and the Great Doxology, and the rest of the service according to the rule.
The Lesser Feasts have two signs: three dots in incomplete circles, one is red (IV in this Service Book). On these feasts, at Vespers, the usual kathisma, at Lord, I have called ... stichera on 6, and at Matins, the Canon on 6, and the Great Doxology, and the rest of the service according to the rule. The black one (V in this Service Book) indicates that at Vespers, at Lord, I have called . . . stichera on 6, at Matins, the Canon on 6, and the Liturgy according to the order of the rule. Those not having a sign have only 4 stichera and the Canon on 4 at Matins.
The English letters a, g, f, e, d, c, and b have been used in the calendar section of this Service Book to accompany the dates and to stand for the letters and respectively of the Slavonic Sluzhebnik calendar sections.