In his “Note on the Maya Eclipse Table of the Dresden Codex” (American Antiquity, Vol. XIV, p. 61, July, 1948) Dr. Satterthwaite “submits that we ought to have a demonstration” of the range of moon phase lengths, also of the three-day named tzolkin periods within which Robert H. Merrill locates on the one hand possible eclipses, and on the other the average three-day length of moon disappearance “if such a double function of the three-day groups is a possibility to be reckoned with.”

On page 39 of American Antiquity for July, 1946, my Moon Chart (Fig. 7) was drawn with sufficient accuracy to show each lunation to scale in tenths of a day, for the arbitrary sample period 1900–33. This covers a like time span to that of the codex lunar table. To show in detail the simple calculations and the graphical accuracy, a sample work sheet is here appended (Fig. 62).