[22] According to modern calculations, the period of the lunar revolution is 29.530588, or approximately 29½ days. For 405 revolutions the accumulated error would be .03×405=12.15 days. This error the Maya obviated by using 29.5 in some calculations and 29.6 in others, the latter offsetting the former. Thus the first 17 revolutions of the sequence are divided into three groups; the first 6 revolutions being computed at 29.5, each giving a total of 177 days; and the second 6 revolutions also being computed at 29.5 each, giving a total of another 177 days. The third group of 5 revolutions, however, was computed at 29.6 each, giving a total of 148 days. The total number of days in the first 17 revolutions was thus computed to be 177+177+147=502, which is very close to the time computed by modern calculations, 502.02.
[23] This is the tropical year or the time from one equinox to its return.
[24] Landa, 1864: p. 52.
[25] Cogolludo, 1688: I, lib. IV, V, p. 186.
[26] For example, if the revolution of Venus had been the governing phenomenon, each monument would be distant from some other by 584 days; if that of Mars, 780 days; if that of Mercury, 115 or 116 days, etc. Furthermore, the sequence, once commenced, would naturally have been more or less uninterrupted. It is hardly necessary to repeat that the intervals which have been found, namely, 7200 and 1800, rest on no known astronomical phenomena but are the direct result of the Maya vigesimal system of numeration.
[27] It is possible that the Codex Peresianus may treat of historical matter, as already explained.
[28] Since the sequence of the twenty day names was continuous, it is obvious that it had no beginning or ending, like the rim of a wheel; consequently any day name may be chosen arbitrarily as the starting point. In the accompanying example
Kan has been chosen to begin with, though Bishop Landa (p. 236) states with regard to the Maya: "The character or letter with which they commence their count of the days or calendar is called Hun-ymix [i. e. 1 Imix]". Again, "Here commences the count of the calendar of the Indians, saying in their language Hun Imix (*) [i. e. 1 Imix]." (Ibid., p. 246.)
[29] Professor Seler says the Maya of Guatemala called this period the kin katun, or "order of the days." He fails to give his authority for this statement, however, and, as will appear later, these terms have entirely different meanings. (See Bulletin 28, p. 14.)