Morgan MS G.44:
A Gospel lectionary produced at the Abbey of St. Peter in Salzburg, ca. 1050.
  f. 2v:A multi-vignette miniature depicting the Nativity, the Annunciation to the Shepherds and the bathing of the infant Jesus with Joseph to the side.
  f. 3: The Gospel reading according to Matthew for the Vigil of Christmas, the opening text of this book.

Calendars are expected components of the missal and the breviary (but not of their correlating chant books, the gradual and the antiphonal). The calendar retains the beginning of the Roman year with 1 January, while the liturgical year, originally understood to begin at Christmas, eventually between the ninth and the eleventh centuries settled on the pre-Christmas period of preparation as its beginning, whether that period was taken to last four weeks or six (as was normal in Spain). Thus, the texts of missals and breviaries begin with Advent (in the temporale) and, usually, the feast of St. Andrew (30 November; in the sanctorale).

Another anomaly is the martyrology: not strictly speaking a liturgical book, it nevertheless may have a calendar at the beginning, although its text doesn't necessarily begin at Advent as in other liturgical books. The calendar-like material that precedes each day's list of saints in a martyrology gives the phase of the moon.

The main feature of the calendar in a liturgical book is that it is perpetual. Because of this, it cannot associate names of the days with the sequential list of days in each month, nor can it include the moveable feasts of the temporale. These vital questions --which day is Sunday? which day is Easter?-- are addressed by means of the Golden Numbers and the Dominical Letters, which usually appear in the calendar in the two first columns on the left in the presentation of each month.

The Golden Numbers represent the 19-year solar cycle and its 235 lunations that bring the sun and the moon back into perfect reconciliation; the system allows one to predict the "Paschal Term," which is to say the full moon that controls Easter (since Easter must occur after the first full moon that is on or after the spring equinox). To predict the actual date of the Sunday that is Easter, one then turns to the Dominical Letters. These are the seven letters, A-G, in the second column on the left, in which the letter A is often larger or more elaborate than the others; beginning with A on 1 January, the letters repeat in the same sequence for all 52 weeks + 1 day of the year. Because of this one extra day, 1 January moves ahead by one named day each year: in 2001, 1 January was a Monday, in 2002 it fell on a Tuesday. Thus 2001 was a G year (since its first Sunday fell on the 7th day after 1 January; all other Sundays of the year, including Easter Sunday, will continue that sequence), 2002 is an F year (since its first Sunday fell six days after 1 January), 2003 will be an E year, and so on.

More than one inexperienced scholar has taken the decorative A on 1 January to represent a real Sunday and thus dated his manuscript to one of the several possible years when Sunday fell on the first of the year. Another pitfall for the unwary lies in the occasional presence of an entry for "Resurrectio Domini" on 27 March; the entry sometime reads, with more accuracy, "Resurrectio Domini vera," meaning that in the year 33, the first Easter Sunday occurred on that date.

X936.C28, f. 1:A missal from 15th century Germany, with the calendar page for January in columns from the left: the Golden Numbers; the Dominical Letters; the Roman system of kalends, nones and ides; the saints with the more important entries in red (red letter days). Plimpton MS 176, f. 5:A calendar produced in Switzerland in 1426, with the Dedication of the church of Constance (9 September) written by the same scribe as the bulk of the text.
Western MS 31, p. 406:A computistical and theological compendium copied in the Low Countries ca. 1450-75, with several dates given for Christ's passion, according to Theophilus, according to Jerome, according to Hugh of St. Victor, and according to "others." Plimpton MS 135, f. 16: A grammar copied in Italy in 1503 with a chart giving the numeric date equivalencies for the designations in Roman style by kalends, nones and ides.