Editing Dominical letter (section)

== History and arrangement ==
According to {{harvnb|Thurston|1909|p=109}} dominical letters are:{{quotation|1=

a device adopted from the Romans by the old chronologers to aid them in finding the day of the week corresponding to any given date, and indirectly to facilitate the adjustment of the 'Proprium de Tempore' to the 'Proprium Sanctorum' when constructing the ecclesiastical calendar for any year. The Church, on account of her [[Liturgical year|complicated system of movable and immovable feasts]]... has from an early period taken upon herself as a special charge to regulate the measurement of time. To secure uniformity in the observance of feasts and fasts, she began, even in the patristic age, to supply a ''computus'', or system of reckoning, by which the relation of the solar and lunar years might be accommodated and the celebration of Easter determined. Naturally she adopted the astronomical methods then available, and these methods and the terminology belonging to them having become traditional, are perpetuated in a measure to this day, even after the reform of the calendar, in the prolegomena to the Breviary and Missal.}}

{{quotation|1=The Romans were accustomed to divide the year into [[Roman calendar#Nundinal cycle|''nundinæ'']], periods of eight days; and in their marble ''[[fasti]]'', or [[calendar]]s, of which numerous specimens remain, they used the first eight letters of the alphabet [A to H] to mark the days of which each period was composed. When the Oriental seven-day period, or week, was introduced in the time of [[Augustus]], the first seven letters of the alphabet were employed in the same way to indicate the days of the new division of time. In fact, fragmentary calendars on marble still survive in which both a cycle of eight letters – A to H – indicating ''nundinae'', and a cycle of seven letters – A to G – indicating weeks, are used side by side (see "Corpus Inscriptionum Latinarum", 2nd ed., I, 220. -The same peculiarity occurs in the [[Philocalian Calendar]] of A.D. 356, ibid., p. 256). This device was imitated by the Christians, and in their calendars the days of the year from 1 January to 31 December were marked with a continuous recurring cycle of seven letters: A, B, C, D, E, F, G. A was always set against 1 January, B against 2 January, C against 3 January, and so on. Thus F fell to 6 January, G to 7 January; A again recurred on 8 January, and also, consequently, on 15 January, 22 January, and 29 January. Continuing in this way, 30 January was marked with a B, 31 January with a C, and 1 February with a D. Supposing this to be carried on through all the days of an [[common year|ordinary year]] (i.e. not a leap year), it will be found that a D corresponds to 1 March, G to 1 April, B to 1 May, E to 1 June, G to 1 July, C to 1 August, F to 1 September, A to 1 October, D to 1 November, and F to 1 December – a result which [[Guillaume Durand|Durandus]] recalled by the following [[distich]]:

Alta Domat Dominus, Gratis Beat Equa Gerentes 
Contemnit Fictos, Augebit Dona Fideli.}}

Another one is "Add G, beg C, fad F," and yet another is "At Dover dwell George Brown, Esquire; Good Christopher Finch; and David Fryer."