There are some reasons why the Universal Unit System assumes not 12^12 but 12^8 a prefix interval.
(1) 12^8 is led naturally by relations between fundamental constants as I explained before
Mass and amount of substance are three dimensional quantities. Therefore,
an atomic scale mass unit should be triple atomic quantity of human scale mass unit, and
an atomic scale amount of substance unit should be triple atomic quantity of human scale amount of substance unit.
An atomic scale mass unit has to be an atomic mass unit, and
an atomic scale amount of substance unit has to be reciprocal Avogadro constant.
These relations require that an atomic factor cannot help becoming not 12^-12 but 12^-8.
(2) 12^4 is a upper limit as for the ratio of quantities that a human being can feel intuitionally.
The human being can grasp numbers only countable in a work day or a night intuitively.
(Example: step counts per day, number of sheep to count at a night)
We cannot but grasp the further numbers logarithmically.
Therefore I gave quantities to become the base points and designed to express
all quantities between the upper and lower 12^4 of these base points.
The interval between these base points becomes bigger, the expression becomes more intuitive.
This is because situation using the same base point becomes frequent.
We come to recognize these base points as XX scale. (such as cosmic scale, atomic scale, ..)
It is easy to recognize the relations of atomic km and atomic dm if used to harmonic km and harmonic dm.
However, we cannot adopt 12^12 as the base point interval because 12^6 exceeds the limit that we can grasp intuitively.
(3) 12^8 and myriad system
have high affinity.
SI definition document
2.2.2 explains derived units with special names and symbols.
Without the special reason including the influence on health of the human body,
The SI did not give new special names to derived units.
It is expensive to add new words to common vocabulary.
Because the new words disturb the spread,
I designed the Universal Unit System to add new words as few as possible.
In addition, I reused the words that there had been already in common vocabulary
based on the commonality of the meaning. (such as 1000-ness)
But I designed the prefix system so that slight difference in expression
did not bring big difference in content.
Therefore, I adopted entirely different words in 12^3 and 12^-3.
Unfortunately because there is no single word with 10000-ness except 'myriad'
in common vocabulary, I cannot give single word expressions to 12^4 and 12^-4.
Expression of 12^4 is longer than expression of 12^8.
This is a left problem.
First Paragraphs are edited 2011-11-27
Decimal figures are indicated by a period “.” as the radix point, and duodecimal figures are indicated by a semicolon“;” as the radix point. Both notations may use a comma “,” and “_” as the digit group separator. ‘X’ expresses ten, ‘E’ expresses eleven and ‘M’ expresses 1_0000,0000;(=12.^8). Octal figures are indicated by an at sign “@” as the radix point.