Ad feriam cuiusque inueniendam hec est facta figura...et hanc rursum repetas.
A (text to "Sequens..."; tables); B (text following "Sequens..."; part of left hand table).
This table corresponds to the Dominical Letter key-letter column in the calendar. The explanatory text advises the reader who wishes to ascertain the weekday of any calendar date to look in the calendar (uide in annali ) and find the Dominical Letter next to the desired date. To convert the Dominical Letter into the weekday using this table, one must also know the position of the annus domini within the 28-year solar cycle. The standard formula, as found, for instance, in Helperic's De computo, is to add 9 to the AD year (1 AD was year 10 of the cycle) and divide by 28; the remainder is the year of the solar cycle.
One can then use the table on the left to find the weekday corresponding to the solar year.
In leap years, one uses the small table in the centre of this page for the period up to the intercalation on 24 February. For example, 1112 is a leap year, and year 1 of the solar cycle. Because the solar year is 52 weeks plus one day long, 1 January and 31 December fall on the same weekday, and will therefore have the same Dominical Letter (A). The table on the left indicates that "A" in year 28 of the cycle (1111) fell on Sunday, so A=1 January in 1112 will be Monday. In the small table, locate Monday, i.e. "F<eria>II", in the left hand column, and read across to find "A". This column, headed by the number "III" applies to 1112 up to 24 February ; after that date, one switches back to the main table on the left, where in year 1, "A" falls on Tuesday.
The table on the right is not mentioned in the text, but it illustrates the other two, and can substitute for them. The small letters in the top row are the Dominical Letters for year 28 of the solar cycle, when "A" is Sunday. The larger letters underneath denote the valid Dominical Letters in year 1 up to the 24 February intercalation (notice the "B<issextus>" in the margin), while those in the row actually labelled "I" are valid for the period following the bissextus. The table is designed, in fact, for a year beginning in 1 March, a usage followed by Abbo of Fleury, for in this case, year 28 is bissextile. Manuscript evidence suggests that this table was Abbo's invention. All three tables, together with the explanatory text found in MS 17, though with the rubric Litterae huius laterculi qui uocatur ratio septizodii...appear in Berlin 138 fol. 29r-v, Vatican City BAV Reg. lat. 309 148v-149r, as well as Noviomagus fols.<12v-13r>. This ensemble, minus the right hand table, is found in Bern 250 fol. 23v. Text, centre table, and right hand table appear in Paris Bibliothèque nationale lat. 7299A fols. 17v and 49v, and in PL 90.819-820. On the other hand, Carolingian computi like Paris, Bibliothèque nationale nouv. acq. lat. 1615fol. 136v, lat. 5239 fol. 136v, and lat. 5543 fol. 94r have only the centre and left tables, and no text (though the ratio septizodii rubric is present). PL 90.734 contains only the centre table. Some 11th and 12th century manuscripts continue this pre-Abbonian tradition, e.g.
Oxford Bodleian Library Bodley 309 fol. 3r, Munich CLM 4563 fol. 10r, and Paris Bibliothèque nationale lat. 15170 fol. 139v.
MS 17's text of Helperic, fol. 130v; the text in PL 139.38 gives the incorrect divisor of 17.