At the center of the Aztec Calendar there is the face of Tonatiuh (face of Sun or Lord of Heaven) around which takes place all daily and periodic phenomena. The crown, nose-pendant, earrings and necklace are magnificent, as must be the ornaments, characteristic of this deity. 
The hair is blond, due to the golden appearance of the sun. The wrinkles on the face show age and maturity. And the tongue, stuck out is the form of an obsidian knife, indicates that the deity demands to be fed with blood and human hearts.
 

The Aztec Calendar's design is based on a set of concentric rings, divided into eight segments. The concentric ring around the face of Tonatiuh consists of the Nahui Olin, signifying 4x movement.

The four square-like spaces contain the glyphs for:
a) Nahui Ocelot (4x Tiger)
b) Nahui Ehecatl (4x Wind)
c) Nahui Quiahuitl (4x Rain)
d) Nahui Atl or Atonatiuh (4x Water)
Other symbols:
e) Double lunar-solar ray
f) Breastplate with two quincunx
g) five feather like figures representing the quantities of 52 and 104 (as well as other designated sums).
h) The claw-like figures on either side of the face represent an eagle, clutching human hearts, and a sacrifice to the Sun.
i) the 5 circles represent specific numerical quantities.

First Ring - from Center. The four Olin symbols framing the center represents the current epoch: Earthquake Sun. The four epochs depicted inside the square portions of this symbol correspond to the four previous epochs, also called Suns. The Aztecs believed that the world was destroyed and re-created four times previous to the current epoch. They believe the current epoch will be destroyed by earthquakes.

a) Nahui Ocelot
(4x Tiger)

First epoch

Ocelotonatjuh (The Jaguar Sun).  Was the first and most remote of the four cosmogonical epochs in which lived the giants created by the gods. They did not till the soil, lived in caves, ate wild fruits and roots, and were in the end attacked and devoured by the jaguars. This basic epoch of the Aztecs is related to the geological quaternary period. As indicated by the discovery of bones of pre-diluvian animals found in deep ravines under dense Lithospheric layers.

b) Nahui Ehecatl
(4x Wind)

Second Epoch

Ehecatonatiuh (The Winds Sun) Second Mythical Epoch. The human race was in danger of being destroyed by tremendous hurricanes, but the gods transformed men into apes so they could hold on better
with four hands and not be carried away by hurricanes. This is the reason for the resemblance between men and simians. The epoch received its name because they found huge forests flattened by cyclones.

c) Nahui Quiahuitl
(4x Rain)

Third epoch

Quiauhtonatiuh (Rain of Fire Sun). Third cosmogonical epoch, in which everything is extinguished by rain of lava and fire.  Men were transformed at this time into birds, thus being saved from the cataclysm. They justified this belief with the traces of volcanic activity and with the discovery of numerous huts and skeletons buried under layers of lava and ashes.

d) Nahui Atl
(4x Water)

Fourth Epoch

Antonatiuh (Water Sun).  Means the fourth epoch, at the end of which everything perished because of terrific storms and torrential rains that covered the whole earth, reaching the peaks of the highest mountains. The gods changed men into fishes to save then from this universal deluge. The discovery of different fossilised species of marine fauna on the tops of mountains created the basis for this belief.

Nahui-Olin

Fifth and last Epoch

Nahui-Olin (Earthquakes Sun). Fifth epoch in the solar age, the next and last destruction of human life in the world. This symbol is used here as a frame for central signs. (points to frame around the squares in the 2nd ring, or the space below the square at 7 o'clock)

The day glyphs

There are twenty day glyphs identified in this ring. The pointer does not actually point towards a specific glyph, but rather it is aimed between the glyph numbers 1 and 20.

1st day: Cipactli (Crocodile)
2nd day: Ehecatl (Wind)
3rd day: Calli (Underworld/House)
4th day: Cuetzapallin (Ripeness/Lizard)
5th day: Coatl (Snake)
6th day: Miquiztli (Death)
7th day: Mazatl (Deer)
8th day: Tochtli (Rabbit)
9th day: Atl (Water)
10th day: Itzcuintli (Dog)

11th day: Ozomatli (Monkey)
12th day: Malinalli (Grass / Dry Herb)
13th day: Acatl (Reed/Cane)
14th day: Ocelotl (Jaguar)
15th day: Cuauhtli (Eagle)
16th day: Cozcacuauhtil (Owl/Vulture)
17th day: Olin (Movement/Earthquake)
18th day: Tecpatl (Obsidian Knife / Stone)
19th day: Quiahuitl (Rain)
20th day: Xochitl (Lord/Flower), last day of the month