D'ni numerals
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D'ni numerals overview
D'ni numerals are a base-25 counting system used by the fictional D'ni race and seen in the two computer games Riven and Uru: Ages Beyond Myst, and in Cyan's Myst novels.
It is suggested that you do not read this article or look at the accompanying picture until you have finished the game Riven. A significant part of the Riven endgame is locked until the player has deduced the meaning of the symbols as numerals, and their values.
The numerals also make a cameo appearance in Myst III: Exile. The meanings of numerals one through eight are presented much more straightforwardly in the Relto Age in Uru: Ages Beyond Myst.
The image to the right from Garternay.com gives you a basic idea of this system. The numerals 1, 2, 3, and 4 are rotated 90 degrees to yield the numerals 5, 10, 15, and 20 respectively. (This principle of Fives misleads many to believe that D'ni numerals are base-5.) These eight numerals are combined to yield numerals for all the numbers zero through twenty-four.
An easy way to calculate the decimal value (base 10, which is normally used in everyday life) is as follows:
([Rotated Number] x 5) + [Normal Number]
If there are two places in the number, (anything over 24) the first square is calculated as above, multiplied by 25, then added to the value of the first box.
Two additional numerals, a 25 (an 'X' with the square box) and a "cyclical zero" (a forward slash with the square box), are commonly used for special purposes.