by dizzark
The Tzolkin is a mayan (and not aztec) calendar featuring a 20 months gear connected to a 13 days gear. It generates a total of 260 unique days.The gear in the game are absolutely connected with the Tzolkin calendar, but for the gameplay purpose and for production simplicity it has been reduced to only one gear featuring 26 cogs that represent the 260 original days... Also when you actually play and move the calendar by one day, you count the 13 days as they would pass in the Tzolkin calendar.... you just don't see the month symbol associated.
As for the wheel image... yes it's an image taken from an Aztec wheel... used on purpose because any tv show or magazine features that image as it was a mayan one. Consider also that Aztec took this kind of stuff from the mayan civilization.