Of the b and a classes from the earliest period to the 9th century inclusive are numbered 1 to 49; those of the 10th century 50 to 99; for the later centuries numbers of three figures are used, and the choice is made so that the figure in the hundreds' place indicates the century, 1 meaning lith century, meaning 12th century, and so on; to all these numbers the appropriate letter, if it be 5 or a, must be always prefixed, but if it be only when there is any chance of ambiguity.
Of the b and a classes from the earliest period to the 9th century inclusive are numbered 1 to 49; those of the 10th century 50 to 99; for the later centuries numbers of three figures are used, and the choice is made so that the figure in the hundreds' place indicates the century, 1 meaning lith century, meaning 12th century, and so on; to all these numbers the appropriate letter, if it be 5 or a, must be always prefixed, but if it be only when there is any chance of ambiguity.