20 glyphs in the 1st period of the E calendar in a way predicts how after 10 periods sun will reach 'harbour' (henua ora). Maybe 2 glyphs corresponds to 1 period? That is probably not so, because 20 presumably represents 20 periods - 10 up to the midpoint and 10 after the midpoint. Or to be more precise: the 10th period has passed the midpoint and the 20th period has passed the end of the next half.

10 means one more than full, which of course is true if we regard 9 as the measure for full - there are no higher digits. 20 means that the limit has passed once more, and as there are two 'years' in a year 20 is the proper symbol.

The Mayan number symbol for 10 has a fleshless jawbone - a sign of death: