Maya numerals
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The ancient Maya civilization used a vigesimal (base-20) numeral system.
The numerals are made up of three symbols; zero (egg shape), one (a dot) and five (a bar).
For example, 19 is written as four dots in a horizontal row above three horizontal lines stacked upon each other.
Digits are stacked with the higher significant digits at the top. Thus, two dots above each other would be read as 1×20 + 1 = 21.
The second place value is not 20×20 = 400, as would be expected, but 18×20, so that one dot over two zeros signifies 360. This is supposed to be because 360 was an early approximation to the number of days in the solar year (the Maya later refined this calculation to a very accurate 365.2422 days). Subsequent place values return to base 20.
Other than the bar and dot notation, Maya numerals can be illustrated by face type glyphs.
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