Mayan Zodiac Calculator

This works out the Maya day sign for a date from the 260 day Tzolkin count. Enter a date and choose a correlation constant, and it returns the day sign and its number, the position in the 260 day round, the Haab date and the full Long Count. The arithmetic runs through the Julian Day Number and the Goodman-Martinez-Thompson constant of 584283 by default, which is the value that matches the count still kept in the Guatemalan highlands and which puts 21 December 2012 on 13.0.0.0.0, 4 Ahau 3 Kankin. Other published tables anchor the count one or two days differently and will name a neighbouring sign, so the constant used is printed with the answer. The count itself is exact, but the character attached to each sign is folklore, so treat that part as entertainment.