"Surely You're Joking, Mr. Feynman!" - unam.

then there were multiples of 13 x 2920 for a while, and then ­­ funny numbers! They were
errors, as far as I could tell. Only many years later did I figure out what they were.
Because figures denoting days were associated with this 584 which was divided
up so peculiarly, I figured if it wasn't some mythical period of some sort, it might be
something astronomical. Finally I went down to the astronomy library and looked it up,
and found that 583.92 days is the period of Venus as it appears from the earth. Then the
236, 90, 250, 8 became apparent: it must be the phases that Venus goes through. It's a
morning star, then it can't be seen (it's on the far side of the sun); then it's an evening star,
and finally it disappears again (it's between the earth and the sun). The 90 and the 8 are
different because Venus moves more slowly through the sky when it is on the far side of
the sun compared to when it passes between the earth and the sun. The difference
between the 236 and the 250 might indicate a difference between the eastern and western
horizons in Maya land.
I discovered another table nearby that had periods of 11,959 days. This turned out
to be a table for predicting lunar eclipses. Still another table had multiples of 91 in
descending order. I never did figure that one out (nor has anyone else).
When I had worked out as much as I could, I finally decided to look at the
Spanish commentary to see how much I was able to figure out. It was complete nonsense.
This symbol was Saturn, this symbol was a god ­­ it didn't make the slightest bit of sense.
So I didn't have to have covered the commentary; I wouldn't have learned anything from
it anyway.
After that I began to read a lot about the Mayans, and found that the great man in
this business was Eric Thompson, some of whose books I now have.
When Nina Byers called me up I realized that I had lost my copy of the Dresden
Codex. (I had lent it to Mrs. H. E. Robertson, who had found a Mayan codex in an old
trunk of an antique dealer in Paris. She had brought it back to Pasadena for me to look at
­­ I still remember driving home with it on the front seat of my car, thinking, "I've gotta
be careful driving: I've got the new codex" ­­ but as soon as I looked at it carefully, I
could see immediately that it was a complete fake. After a little bit of work I could find
where each picture in the new codex had come from in the Dresden Codex. So I lent her
my book to show her, and I eventually forgot she had it.) So the librarians at UCLA
worked very hard to find another copy of Villacorta's rendition of the Dresden Codex,
and lent it to me.
I did all the calculations all over again, and in fact I got a little bit further than I
did before: I figured out that those "funny numbers" which I thought before were errors
were really integer multiples of something closer to the correct period (583.923) ­­ the
Mayans had realized that 584 wasn't exactly right!*
*While I was studying this table of corrections for the period of Venus, I discovered a rare
exaggeration by Mr. Thompson. He wrote that by looking at the table, you can deduce how the
Mayans calculated the correct period of Venus ­­ use this number four times and that difference
once and you get an accuracy of one day in 4000 years, which is really quite remarkable,
especially since the Mayans observed for only a few hundred years.
Thompson happened to pick a combination which fit what he thought was the right period
for Venus, 583.92. But when you put in a more exact figure, something like 583.923, you find the
Mayans were off by more. Of course, by choosing a different combination you can get the
numbers in the table to give you 583.923 with the same remarkable accuracy!