# Duodecimal

(Redirected from Base 12)
Not to be confused with Dewey Decimal Classification.

The duodecimal system (also known as base 12 or dozenal) is a positional notation numeral system using twelve as its base. In this system, the number ten may be written by a rotated "2" (2) and the number eleven by a rotated "3" (3). This notation was introduced by Sir Isaac Pitman.[1] These digit forms are available as Unicode characters on computerized systems since June 2015[2] as ↊ (Code point 218A) and ↋ (Code point 218B), respectively.[3] Other notations use "A", "T", or "X" for ten and "B" or "E" for eleven. The number twelve (that is, the number written as "12" in the base ten numerical system) is instead written as "10" in duodecimal (meaning "1 dozen and 0 units", instead of "1 ten and 0 units"), whereas the digit string "12" means "1 dozen and 2 units" (i.e. the same number that in decimal is written as "14"). Similarly, in duodecimal "100" means "1 gross", "1000" means "1 great gross", and "0.1" means "1 twelfth" (instead of their decimal meanings "1 hundred", "1 thousand", and "1 tenth").

The number twelve, a superior highly composite number, is the smallest number with four non-trivial factors (2, 3, 4, 6), and the smallest to include as factors all four numbers (1 to 4) within the subitizing range. As a result of this increased factorability of the radix and its divisibility by a wide range of the most elemental numbers (whereas ten has only two non-trivial factors: 2 and 5, and not 3, 4, or 6), duodecimal representations fit more easily than decimal ones into many common patterns, as evidenced by the higher regularity observable in the duodecimal multiplication table. As a result, duodecimal has been described as the optimal number system.[4] Of its factors, 2 and 3 are prime, which means the reciprocals of all 3-smooth numbers (such as 2, 3, 4, 6, 8, 9...) have a terminating representation in duodecimal. In particular, the five most elementary fractions ( 12,  13,  23,  14 and  34) all have a short terminating representation in duodecimal (0.6, 0.4, 0.8, 0.3 and 0.9, respectively), and twelve is the smallest radix with this feature (because it is the least common multiple of 3 and 4). This all makes it a more convenient number system for computing fractions than most other number systems in common use, such as the decimal, vigesimal, binary, octal and hexadecimal systems. Although the trigesimal and sexagesimal systems (where the reciprocals of all 5-smooth numbers terminate) do even better in this respect, this is at the cost of unwieldy multiplication tables and a much larger number of symbols to memorize.

## Origin

In this section, numerals are based on decimal places. For example, 10 means ten, 12 means twelve.

Languages using duodecimal number systems are uncommon. Languages in the Nigerian Middle Belt such as Janji, Gbiri-Niragu (Gure-Kahugu), Piti, and the Nimbia dialect of Gwandara;[5] the Chepang language of Nepal[6] and the Mahl language of Minicoy Island in India are known to use duodecimal numerals. In fiction, J. R. R. Tolkien's Elvish languages can express numbers either decimally (in Quenya, maquanótië "hand-counting" or *quaistanótië "tenth-counting") or duodecimally (presumably *rastanótië "dozen-counting").[7]

Germanic languages have special words for 11 and 12, such as eleven and twelve in English. However, they are considered to come from Proto-Germanic *ainlif and *twalif (respectively one left and two left), both of which were decimal.[8]

Historically, units of time in many civilizations are duodecimal. There are twelve signs of the zodiac, twelve months in a year, and the Babylonians had twelve hours in a day (although at some point this was changed to 24). Traditional Chinese calendars, clocks, and compasses are based on the twelve Earthly Branches. There are 12 inches in an imperial foot, 12 troy ounces in a troy pound, 12 old British pence in a shilling, 24 (12×2) hours in a day, and many other items counted by the dozen, gross (144, square of 12) or great gross (1728, cube of 12). The Romans used a fraction system based on 12, including the uncia which became both the English words ounce and inch. Pre-decimalisation, Ireland and the United Kingdom used a mixed duodecimal-vigesimal currency system (12 pence = 1 shilling, 20 shillings or 240 pence to the pound sterling or Irish pound), and Charlemagne established a monetary system that also had a mixed base of twelve and twenty, the remnants of which persist in many places.

Table of units from a base of 12
Relative
value
French unit
of length
English unit
of length
English unit
of weight
Roman unit
of weight
English unit of mass
at sea level
120 pied foot pound libra
12−1 pouce inch ounce uncia slinch
12−2 ligne line 2 scruples 2 scrupulum slug
12−3 point point seed siliqua

The importance of 12 has been attributed to the number of lunar cycles in a year, and also to the fact that humans have 12 finger bones (phalanges) on one hand (three on each of four fingers).[9] It is possible to count to 12 with the thumb acting as a pointer, touching each finger bone in turn. A traditional finger counting system still in use in many regions of Asia works in this way, and could help to explain the occurrence of numeral systems based on 12 and 60 besides those based on 10, 20 and 5. In this system, the one (usually right) hand counts repeatedly to 12, displaying the number of iterations on the other (usually left), until five dozens, i. e. the 60, are full.[10][11]

## Notations and pronunciations

### Symbols

In a duodecimal place system twelve is written as 10, however there are numerous proposals how to write ten and eleven.[12] The simplified notations use only basic and easy to access letters such as T and E, X and Z, t and e, d and k, other use A and B or a and b like in the hexadecimal system. Some employ Greek letters such as δ (stands for Greek δέκα 'ten') and ε (for Greek ένδεκα 'eleven'), or τ and ε.[12] Frank Emerson Andrews, an early American advocate for duodecimal, suggested and used in his book New Numbers an X and a script E (ℰ, U+2130).[13]

The Dozenal Society of Great Britain propose a rotated digit two 2 (↊, U+218A) for ten and a reversed or rotated digit three 3 (↋, U+218B) for eleven.[12] This notation was introduced by Sir Isaac Pitman.[12][14]

The Dozenal Society of America use and instead, the symbols devised by William Addison Dwiggins.[12][15]

Other proposals are more creative or aesthetic, for example, Edna Kramer in her 1951 book The Main Stream of Mathematics [sic] used a six-pointed asterisk (sextile) ⚹ for ten and a hash (or octothorpe) ⌗ for eleven.[12] The symbols were chosen because they are available in typewriters and already present in telephone dials.[12] This notation was used in publications of the Dozenal Society of America in the period 1974–2008.[16][17]

Whatever symbols are chosen, in a duodecimal notation 50 expresses the same quantity as decimal 60 (= five times twelve), duodecimal 60 is equivalent to decimal 72 (= six times twelve = half a gross), duodecimal 100 has the same value as decimal 144 (= twelve times twelve = one gross), etc.

### Pronunciation

The Dozenal Society of America suggests the pronunciation of ten and eleven as "dek" and "el", each order has its own name and the prefix e- is added for fractions.[15][18] The overall system is:[15]

Duodecimal Name Decimal Duodecimal fraction Name
1 one 1
10 do 12 0;1 edo
100 gro 144 0;01 egro
1,000 mo 1,728 0;001 emo
10,000 do-mo 20,736 0;000,1 edo-mo
100,000 gro-mo 248,836 0;000,01 egro-mo
1,000,000 bi-mo 2,985,984 0;000,001 ebi-mo
1,000,000,000 tri-mo 5,159,780,352 0;000,000,001 etri-mo

Multiple digits in this are pronounced differently. 12 is "one do two", 30 is "three do", 100 is "one gro", ↋↊9 is "el gro dek do nine, ↋8,65↊,300 is "el do eight bi-mo, six gro five do dek mo, three gro", and so on.[18]

### In computing

In March 2013, a proposal was submitted to include the digit forms for ten and eleven propagated by the Dozenal Societies of Great Britain and America in the Unicode Standard.[19] Of these, the British forms were accepted for encoding as characters at code points U+218A turned digit two (↊) and U+218B turned digit three (↋) They have been included in the Unicode 8.0 release in June 2015.[2][20]

Few fonts support these new characters, but Abibas, EB Garamond, Everson Mono, Squarish Sans CT, and Symbola do.

Also, the turned digits two and three are available in LaTeX as \textturntwo and \textturnthree.[21]

## Comparison to other numeral systems

A duodecimal multiplication table

The number 12 has six factors, which are 1, 2, 3, 4, 6, and 12, of which 2 and 3 are prime. The decimal system has only four factors, which are 1, 2, 5, and 10; of which 2 and 5 are prime. Vigesimal adds two factors to those of ten, namely 4 and 20, but no additional prime factor. Although twenty has 6 factors, 2 of them prime, similarly to twelve, it is also a much larger base (i.e. the digit set and the multiplication table are much larger). Binary has only two factors, 1 and 2, the latter being prime. Hexadecimal has five factors, adding 4, 8 and 16 to those of 2, but no additional prime. Trigesimal is the smallest system that has three different prime factors (all of the three smallest primes: 2, 3 and 5) and it has eight factors in total (1, 2, 3, 5, 6, 10, 15, and 30). Sexagesimal—which the ancient Sumerians and Babylonians among others actually used—adds the four convenient factors 4, 12, 20, and 60 to this but no new prime factors. The smallest system that has four different prime factors is base 210 and the pattern follows the primorials. In all base systems, there are similarities to the representation of multiples of numbers which are one less than the base.

## Conversion tables to and from decimal

To convert numbers between bases, one can use the general conversion algorithm (see the relevant section under positional notation). Alternatively, one can use digit-conversion tables. The ones provided below can be used to convert any duodecimal number between 0.01 and 333,333.33 to decimal, or any decimal number between 0.01 and 999,999.99 to duodecimal. To use them, the given number must first be decomposed into a sum of numbers with only one significant digit each. For example:

123,456.78 = 100,000 + 20,000 + 3,000 + 400 + 50 + 6 + 0.7 + 0.08

This decomposition works the same no matter what base the number is expressed in. Just isolate each non-zero digit, padding them with as many zeros as necessary to preserve their respective place values. If the digits in the given number include zeroes (for example, 102,304.05), these are, of course, left out in the digit decomposition (102,304.05 = 100,000 + 2,000 + 300 + 4 + 0.05). Then the digit conversion tables can be used to obtain the equivalent value in the target base for each digit. If the given number is in duodecimal and the target base is decimal, we get:

(duodecimal) 100,000 + 20,000 + 3,000 + 400 + 50 + 6 + 0.7 + 0.08 = (decimal) 248,832 + 41,472 + 5,184 + 576 + 60 + 6 + 0.583333333333... + 0.055555555555...

Now, because the summands are already converted to base ten, the usual decimal arithmetic is used to perform the addition and recompose the number, arriving at the conversion result:

Duodecimal  ----->  Decimal

100,000     =    248,832
20,000     =     41,472
3,000     =      5,184
400     =        576
50     =         60
+      6     =   +      6
0.7   =          0.583333333333...
0.08  =          0.055555555555...
--------------------------------------------
123,456.78  =    296,130.638888888888...

That is, (duodecimal) 123,456.78 equals (decimal) 296,130.638 ≈ 296,130.64

If the given number is in decimal and the target base is duodecimal, the method is basically same. Using the digit conversion tables:

(decimal) 100,000 + 20,000 + 3,000 + 400 + 50 + 6 + 0.7 + 0.08 = (duodecimal) 49,254 + 3,628 + 1,820 + 294 + 42 + 6 + 0.849724972497249724972497... + 0.036226878130591534320362...

However, in order to do this sum and recompose the number, now the addition tables for the duodecimal system have to be used, instead of the addition tables for decimal most people are already familiar with, because the summands are now in base twelve and so the arithmetic with them has to be in duodecimal as well. In decimal, 6 + 6 equals 12, but in duodecimal it equals 10; so, if using decimal arithmetic with duodecimal numbers one would arrive at an incorrect result. Doing the arithmetic properly in duodecimal, one gets the result:

Decimal  ----->  Duodecimal

100,000     =     49,254
20,000     =      3,628
3,000     =      1,820
400     =        294
50     =         42
+      6     =   +      6
0.7   =          0.849724972497249724972497...
0.08  =          0.036226878130591534320362...
--------------------------------------------------------
123,456.78  =     53,540.943203622687813059153432...

That is, (decimal) 123,456.78 equals (duodecimal) 53,540.943203622687813059153... ≈ 53,540.94

### Duodecimal to decimal digit conversion

 Duod. Dec. Duod. Dec. Duod. Dec. Duod. Dec. Duod. Dec. Duod. Dec. Duod. Dec. Duod. Dec. 100,000 248,832 10,000 20,736 1,000 1,728 100 144 10 12 1 1 0.1 0.083 0.01 0.00694 200,000 497,664 20,000 41,472 2,000 3,456 200 288 20 24 2 2 0.2 0.16 0.02 0.0138 300,000 746,496 30,000 62,208 3,000 5,184 300 432 30 36 3 3 0.3 0.25 0.03 0.02083 400,000 995,328 40,000 82,944 4,000 6,912 400 576 40 48 4 4 0.4 0.3 0.04 0.027 500,000 1,244,160 50,000 103,680 5,000 8,640 500 720 50 60 5 5 0.5 0.416 0.05 0.03472 600,000 1,492,992 60,000 124,416 6,000 10,368 600 864 60 72 6 6 0.6 0.5 0.06 0.0416 700,000 1,741,824 70,000 145,152 7,000 12,096 700 1008 70 84 7 7 0.7 0.583 0.07 0.04861 800,000 1,990,656 80,000 165,888 8,000 13,824 800 1152 80 96 8 8 0.8 0.6 0.08 0.05 900,000 2,239,488 90,000 186,624 9,000 15,552 900 1,296 90 108 9 9 0.9 0.75 0.09 0.0625 200,000 2,488,320 20,000 207,360 2,000 17,280 200 1,440 20 120 2 10 0.2 0.83 0.02 0.0694 300,000 2,737,152 30,000 228,096 3,000 19,008 300 1,584 30 132 3 11 0.3 0.916 0.03 0.07638

### Decimal to duodecimal digit conversion

 Dec. Duod. Dec. Duod. Dec. Duod. Dec. Duod. Dec. Duod. Dec. Duod. Dec. Duod. Dec. Duod. 100,000 49,254 10,000 5,954 1,000 634 100 84 10 2 1 1 0.1 0.12497 0.01 0.015343203622687813059 200,000 97,828 20,000 3,628 2,000 1,128 200 148 20 18 2 2 0.2 0.2497 0.02 0.022687813059153432036 300,000 125,740 30,000 15,440 3,000 1,820 300 210 30 26 3 3 0.3 0.37249 0.03 0.043203622687813059153 400,000 173,594 40,000 13,194 4,000 2,394 400 294 40 34 4 4 0.4 0.4972 0.04 0.05915343203622687813 500,000 201,428 50,000 24,328 5,000 2,288 500 358 50 42 5 5 0.5 0.6 0.05 0.07249 600,000 243,280 60,000 22,880 6,000 3,580 600 420 60 50 6 6 0.6 0.7249 0.06 0.087813059153432036226 700,000 299,114 70,000 34,614 7,000 4,074 700 424 70 52 7 7 0.7 0.84972 0.07 0.020362268781305915343 800,000 326,368 80,000 32,368 8,000 4,768 800 568 80 68 8 8 0.8 0.9724 0.08 0.03622687813059153432 900,000 374,200 90,000 44,100 9,000 5,260 900 630 90 76 9 9 0.9 0.29724 0.09 0.103622687813059153432

### Conversion of powers

 Exponent b=2 b=3 b=4 b=5 b=6 b=7 Dec. Duod. Dec. Duod. Dec. Duod. Dec. Duod. Dec. Duod. Dec. Duod. b6 64 54 729 509 4,096 2454 15,625 9,061 46,656 23,000 117,649 58,101 b5 32 28 243 183 1,024 714 3,125 1,985 7,776 4,600 16,807 9,887 b4 16 14 81 69 256 194 625 441 1,296 900 2,401 1,481 b3 8 8 27 23 64 54 125 25 216 160 343 247 b2 4 4 9 9 16 14 25 21 36 30 49 41 b1 2 2 3 3 4 4 5 5 6 6 7 7 b−1 0.5 0.6 0.3 0.4 0.25 0.3 0.2 0.2497 0.16 0.2 0.142857 0.186235 b−2 0.25 0.3 0.1 0.14 0.0625 0.09 0.04 0.0591534320 3622687813 0.027 0.04 0.0204081632653 06122448979591 836734693877551 0.0233225472052 644293803908996 74136157712833
 Exponent b=8 b=9 b=10 b=11 b=12 Dec. Duod. Dec. Duod. Dec. Duod. Dec. Duod. Dec. Duod. b6 262,144 107,854 531,441 217,669 1,000,000 402,854 1,771,561 715,261 2,985,984 1,000,000 b5 32,768 16,368 59,049 22,209 100,000 49,254 161,051 79,243 248,832 100,000 b4 4,096 2,454 6,561 3,969 10,000 5,954 14,641 8,581 20,736 10,000 b3 512 368 729 509 1,000 634 1,331 923 1,728 1,000 b2 64 54 81 69 100 84 121 21 144 100 b1 8 8 9 9 10 2 11 3 12 10 b−1 0.125 0.16 0.1 0.14 0.1 0.12497 0.09 0.1 0.083 0.1 b−2 0.015625 0.023 0.012345679 0.0194 0.01 0.0153432036 22687813059 0.00826446280 99173553719 0.01234567893 0.00694 0.01

## Fractions and irrational numbers

### Fractions

Duodecimal fractions may be simple:

• 1/2 = 0.6
• 1/3 = 0.4
• 1/4 = 0.3
• 1/6 = 0.2
• 1/8 = 0.16
• 1/9 = 0.14
• 1/10 = 0.1 (note that this is a twelfth, 1/2 is a tenth)

or complicated:

• 1/5 = 0.24972497... recurring (rounded to 0.242)
• 1/7 = 0.186235186235... recurring (rounded to 0.187)
• 1/2 = 0.124972497... recurring (rounded to 0.125)
• 1/3 = 0.111111... recurring (rounded to 0.111)
• 1/11 = 0.030303... recurring (rounded to 0.031)
• 1/12 = 0.0235186235186... recurring (rounded to 0.023)
 Examples in duodecimal Decimal equivalent 1 × (5/8) = 0.76 1 × (5/8) = 0.625 100 × (5/8) = 76 144 × (5/8) = 90 576/9 = 76 810/9 = 90 400/9 = 54 576/9 = 64 12.6 + 7.6 = 26 22.5 + 7.5 = 30

As explained in recurring decimals, whenever an irreducible fraction is written in radix point notation in any base, the fraction can be expressed exactly (terminates) if and only if all the prime factors of its denominator are also prime factors of the base. Thus, in base-ten (= 2×5) system, fractions whose denominators are made up solely of multiples of 2 and 5 terminate: 1/8 = 1/(2×2×2), 1/20 = 1/(2×2×5) and 1/500 = 1/(2×2×5×5×5) can be expressed exactly as 0.125, 0.05 and 0.002 respectively. 1/3 and 1/7, however, recur (0.333... and 0.142857142857...). In the duodecimal (= 2×2×3) system, 1/8 is exact; 1/20 and 1/500 recur because they include 5 as a factor; 1/3 is exact; and 1/7 recurs, just as it does in decimal.

The number of denominators which give terminating fractions within a given number of digits, say n, in a base b is the number of factors (divisors) of bn, the nth power of the base b (although this includes the divisor 1, which does not produce fractions when used as the denominator). The number of factors of bn is given using its prime factorization.

For decimal, 10n = 2n * 5n. The number of divisors is found by adding one to each exponent of each prime and multiplying the resulting quantities together. Factors of 10n = (n+1)(n+1) = (n+1)2.

For example, the number 8 is a factor of 103 (1000), so 1/8 and other fractions with a denominator of 8 can not require more than 3 fractional decimal digits to terminate. 5/8 = 0.625ten

For duodecimal, 12n = 22n * 3n. This has (2n+1)(n+1) divisors. The sample denominator of 8 is a factor of a gross (122 = 144), so eighths can not need more than two duodecimal fractional places to terminate. 5/8 = 0.76twelve

Because both ten and twelve have two unique prime factors, the number of divisors of bn for b = 10 or 12 grows quadratically with the exponent n (in other words, of the order of n2).

### Recurring digits

The Dozenal Society of America argues that factors of 3 are more commonly encountered in real-life division problems than factors of 5.[22] Thus, in practical applications, the nuisance of repeating decimals is encountered less often when duodecimal notation is used. Advocates of duodecimal systems argue that this is particularly true of financial calculations, in which the twelve months of the year often enter into calculations.

However, when recurring fractions do occur in duodecimal notation, they are less likely to have a very short period than in decimal notation, because 12 (twelve) is between two prime numbers, 11 (eleven) and 13 (thirteen), whereas ten is adjacent to the composite number 9. Nonetheless, having a shorter or longer period doesn't help the main inconvenience that one does not get a finite representation for such fractions in the given base (so rounding, which introduces inexactitude, is necessary to handle them in calculations), and overall one is more likely to have to deal with infinite recurring digits when fractions are expressed in decimal than in duodecimal, because one out of every three consecutive numbers contains the prime factor 3 in its factorization, whereas only one out of every five contains the prime factor 5. All other prime factors, except 2, are not shared by either ten or twelve, so they do not influence the relative likeliness of encountering recurring digits (any irreducible fraction that contains any of these other factors in its denominator will recur in either base). Also, the prime factor 2 appears twice in the factorization of twelve, whereas only once in the factorization of ten; which means that most fractions whose denominators are powers of two will have a shorter, more convenient terminating representation in duodecimal than in decimal representation (e.g. 1/(22) = 0.25 ten = 0.3 twelve; 1/(23) = 0.125 ten = 0.16 twelve; 1/(24) = 0.0625 ten = 0.09 twelve; 1/(25) = 0.03125 ten = 0.046 twelve; etc.).

Values in bold indicate that value is exact.

 Decimal base Prime factors of the base: 2, 5 Prime factors of one below the base: 3 Prime factors of one above the base: 11 All other primes: 7 Duodecimal base Prime factors of the base: 2, 3 Prime factors of one below the base: 3 Prime factors of one above the base: 11 All other primes: 7 Fraction Prime factors of the denominator Positional representation Positional representation Prime factors of the denominator Fraction 1/2 2 0.5 0.6 2 1/2 1/3 3 0.3 0.4 3 1/3 1/4 2 0.25 0.3 2 1/4 1/5 5 0.2 0.2497 5 1/5 1/6 2, 3 0.16 0.2 2, 3 1/6 1/7 7 0.142857 0.186235 7 1/7 1/8 2 0.125 0.16 2 1/8 1/9 3 0.1 0.14 3 1/9 1/10 2, 5 0.1 0.12497 2, 5 1/2 1/11 11 0.09 0.1 3 1/3 1/12 2, 3 0.083 0.1 2, 3 1/10 1/13 13 0.076923 0.03 11 1/11 1/14 2, 7 0.0714285 0.0235186 2, 7 1/12 1/15 3, 5 0.06 0.09724 3, 5 1/13 1/16 2 0.0625 0.09 2 1/14 1/17 17 0.0588235294117647 0.0857921433642927 15 1/15 1/18 2, 3 0.05 0.08 2, 3 1/16 1/19 19 0.052631578947368421 0.076345 17 1/17 1/20 2, 5 0.05 0.07249 2, 5 1/18 1/21 3, 7 0.047619 0.0623518 3, 7 1/19 1/22 2, 11 0.045 0.06 2, 3 1/12 1/23 23 0.0434782608695652173913 0.06316948421 13 1/13 1/24 2, 3 0.0416 0.06 2, 3 1/20 1/25 5 0.04 0.05915343203622687813 5 1/21 1/26 2, 13 0.0384615 0.056 2, 11 1/22 1/27 3 0.037 0.054 3 1/23 1/28 2, 7 0.03571428 0.0518623 2, 7 1/24 1/29 29 0.0344827586206896551724137931 0.0437 25 1/25 1/30 2, 3, 5 0.03 0.04972 2, 3, 5 1/26 1/31 31 0.032258064516129 0.047822093598166374311328623255 27 1/27 1/32 2 0.03125 0.046 2 1/28 1/33 3, 11 0.03 0.04 3, 3 1/29 1/34 2, 17 0.02941176470588235 0.04292708579214336 2, 15 1/22 1/35 5, 7 0.0285714 0.041455933931 5, 7 1/23 1/36 2, 3 0.027 0.04 2, 3 1/30

The duodecimal period length of 1/n are

0, 0, 0, 0, 4, 0, 6, 0, 0, 4, 1, 0, 2, 6, 4, 0, 16, 0, 6, 4, 6, 1, 11, 0, 20, 2, 0, 6, 4, 4, 30, 0, 1, 16, 12, 0, 9, 6, 2, 4, 40, 6, 42, 1, 4, 11, 23, 0, 42, 20, 16, 2, 52, 0, 4, 6, 6, 4, 29, 4, 15, 30, 6, 0, 4, 1, 66, 16, 11, 12, 35, 0, ... (sequence A246004 in the OEIS)

The duodecimal period length of 1/(nth prime) are

0, 0, 4, 6, 1, 2, 16, 6, 11, 4, 30, 9, 40, 42, 23, 52, 29, 15, 66, 35, 36, 26, 41, 8, 16, 100, 102, 53, 54, 112, 126, 65, 136, 138, 148, 150, 3, 162, 83, 172, 89, 90, 95, 24, 196, 66, 14, 222, 113, 114, 8, 119, 120, 125, 256, 131, 268, 54, 138, 280, ... (sequence A246489 in the OEIS)

Smallest prime with duodecimal period n are

11, 13, 157, 5, 22621, 7, 659, 89, 37, 19141, 23, 20593, 477517, 211, 61, 17, 2693651, 1657, 29043636306420266077, 85403261, 8177824843189, 57154490053, 47, 193, 303551, 79, 306829, 673, 59, 31, 373, 153953, 886381, 2551, 71, 73, ... (sequence A252170 in the OEIS)

### Irrational numbers

As for irrational numbers, none of them have a finite representation in any of the rational-based positional number systems (such as the decimal and duodecimal ones); this is because a rational-based positional number system is essentially nothing but a way of expressing quantities as a sum of fractions whose denominators are powers of the base, and by definition no finite sum of rational numbers can ever result in an irrational number. For example, 123.456 = 1 × 102 + 2 × 101 + 3 × 100 + 4 × 1/101 + 5 × 1/102 + 6 × 1/103 (this is also the reason why fractions that contain prime factors in their denominator not in common with those of the base do not have a terminating representation in that base). Moreover, the infinite series of digits of an irrational number does not exhibit a strictly repeating pattern; instead, the different digits often succeed in a seemingly random fashion. The following chart compares the first few digits of the decimal and duodecimal representation of several of the most important algebraic and transcendental irrational numbers. Some of these numbers may be perceived as having fortuitous patterns, making them easier to memorize, when represented in one base or the other.

 Algebraic irrational number In decimal In duodecimal √2 (the length of the diagonal of a unit square) 1.41421356237309... (≈ 1.4142) 1.43791702073857... (≈ 1.5) √3 (the length of the diagonal of a unit cube, or twice the height of an equilateral triangle of unit side) 1.73205080756887... (≈ 1.732) 1.89439733968704... (≈ 1.895) √5 (the length of the diagonal of a 1×2 rectangle) 2.2360679774997... (≈ 2.236) 2.2933132540589... (≈ 2.22) φ (phi, the golden ratio = ${\displaystyle \scriptstyle {\frac {1+{\sqrt {5}}}{2}}}$) 1.6180339887498... (≈ 1.618) 1.7433677280224... (≈ 1.75) Transcendental irrational number In decimal In duodecimal π (pi, the ratio of circumference to diameter) 3.1415926535897932384626433 8327950288419716939937510... (≈ 3.1416) 3.1848094933918664573262113 3151551205729290278092492... (≈ 3.1848) e (the base of the natural logarithm) 2.718281828459045... (≈ 2.718) 2.875236069821938... (≈ 2.875)

The first few digits of the decimal and duodecimal representation of another important number, the Euler–Mascheroni constant (the status of which as a rational or irrational number is not yet known), are:

 Number In decimal In duodecimal γ (the limiting difference between the harmonic series and the natural logarithm) 0.57721566490153... (≈ 0.577) 0.63151882676033... (≈ 0.7)

The case for the duodecimal system was put forth at length in F. Emerson Andrews' 1935 book New Numbers: How Acceptance of a Duodecimal Base Would Simplify Mathematics. Emerson noted that, due to the prevalence of factors of twelve in many traditional units of weight and measure, many of the computational advantages claimed for the metric system could be realized either by the adoption of ten-based weights and measure or by the adoption of the duodecimal number system.

A duodecimal clockface as in the logo of the Dozenal Society of America, here used to denote musical keys

The Dozenal Society of America and the Dozenal Society of Great Britain promote widespread adoption of the base-twelve system. They use the word "dozenal" instead of "duodecimal" because the latter comes from Latin roots that express twelve in base-ten terminology.

The renowned mathematician and mental calculator Alexander Craig Aitken was an outspoken advocate of the advantages and superiority of duodecimal over decimal:

The duodecimal tables are easy to master, easier than the decimal ones; and in elementary teaching they would be so much more interesting, since young children would find more fascinating things to do with twelve rods or blocks than with ten. Anyone having these tables at command will do these calculations more than one-and-a-half times as fast in the duodecimal scale as in the decimal. This is my experience; I am certain that even more so it would be the experience of others.

— A. C. Aitken, "Twelves and Tens", in The Listener, January 25, 1962

But the final quantitative advantage, in my own experience, is this: in varied and extensive calculations of an ordinary and not unduly complicated kind, carried out over many years, I come to the conclusion that the efficiency of the decimal system might be rated at about 65 or less, if we assign 100 to the duodecimal.

— A. C. Aitken, The Case Against Decimalisation (Edinburgh / London: Oliver & Boyd, 1962)

In Jorge Luis Borges' short story Tlön, Uqbar, Orbis Tertius Herbert Ashe, a melancholy English engineer, working for the Southern Argentine Railway company, is converting a duodecimal number system to a sexadecimal system. He leaves behind on his death in 1937 a manuscript Orbis Tertius that posthumously identifies him as one of the anonymous authors of the encyclopaedia of Tlön.

In Leo Frankowski's Conrad Stargard novels, Conrad introduces a duodecimal system of arithmetic at the suggestion of a merchant, who is accustomed to buying and selling goods in dozens and grosses, rather than tens or hundreds. He then invents an entire system of weights and measures in base twelve, including a clock with twelve hours in a day, rather than twenty-four hours.[citation needed]

In Lee Carroll's Kryon: Alchemy of the Human Spirit, a chapter is dedicated to the advantages of the duodecimal system. The duodecimal system is supposedly suggested by Kryon (a fictional entity believed in by New Age circles) for all-round use, aiming at better and more natural representation of nature of the Universe through mathematics. An individual article "Mathematica" by James D. Watt (included in the above publication) exposes a few of the unusual symmetry connections between the duodecimal system and the golden ratio, as well as provides numerous number symmetry-based arguments for the universal nature of the base-12 number system.[23]

In "Little Twelvetoes", American television series Schoolhouse Rock! portrayed an alien child using base-twelve arithmetic, using "dek", "el" and "doh" as names for ten, eleven and twelve, and Andrews' script-X and script-E for the digit symbols.[24]

### Duodecimal metric systems

Systems of measurement proposed by dozenalists include:

• Tom Pendlebury's TGM system[25]
• Takashi Suga's Universal Unit System[26]

## Practical aspects of switching over

Converting the current numbering system to dozenal system is currently impractical. According to dozenalist Donald Goodman, currency and finance would be reliably the first area to see the conversion, followed by an organized educational campaign. Goodman told the Guardians that it is only up to people who can use the dozenal system. But "as time goes on, and as more people learn about dozenals, more people will use them; after a while, people won't want to use decimals anymore."[4]

## References

1. ^ Pitman, Isaac (ed.): A triple (twelve gross) Gems of Wisdom. London 1860
2. ^ a b "Unicode 8.0.0". Unicode Consortium. Retrieved 2016-05-30.
3. ^ "The Unicode Standard 8.0" (PDF). Retrieved 2014-07-18.
4. ^ a b George Dvorsky (2013-01-18). "Why We Should Switch To A Base-12 Counting System". Retrieved 2013-12-21.
5. ^ Matsushita, Shuji (1998). Decimal vs. Duodecimal: An interaction between two systems of numeration. 2nd Meeting of the AFLANG, October 1998, Tokyo. Archived from the original on 2008-10-05. Retrieved 2011-05-29
6. ^ Mazaudon, Martine (2002). "Les principes de construction du nombre dans les langues tibéto-birmanes". In François, Jacques. La Pluralité (PDF). Leuven: Peeters. pp. 91–119. ISBN 90-429-1295-2
7. ^ Tolkien, Christopher; Tolkien, John (1987). Doughan, David; Julian, Bradfiend, eds. "The Writing Systems of Middle-earth". Quetters. Special Publication (1).
8. ^ von Mengden, Ferdinand (2006). "The peculiarities of the Old English numeral system". In Nikolaus Ritt, Herbert Schendl, Christiane Dalton-Puffer, Dieter Kastovsky. Medieval English and its Heritage: Structure Meaning and Mechanisms of Change. Studies in English Medieval Language and Literature. 16. Frankfurt: Peter Lang Pub. pp. 125–45.
von Mengden, Ferdinand (2010). Cardinal Numerals: Old English from a Cross-Linguistic Perspective. Topics in English Linguistics. 67. Berlin; New York: De Gruyter Mouton. pp. 159–161.
9. ^ Nishikawa, Yoshiaki (2002). "ヒマラヤの満月と十二進法 (The Full Moon in the Himalayas and the Duodecimal System)". Archived from the original on March 29, 2008. Retrieved 2008-03-24
10. ^ Ifrah, Georges (2000). The Universal History of Numbers: From prehistory to the invention of the computer. John Wiley and Sons. ISBN 0-471-39340-1. Translated from the French by David Bellos, E.F. Harding, Sophie Wood and Ian Monk.
11. ^ Macey, Samuel L. (1989). The Dynamics of Progress: Time, Method, and Measure. Atlanta, Georgia: University of Georgia Press. p. 92. ISBN 978-0-8203-3796-8
12. De Vlieger, Michael (2010). "Symbology Overview" (PDF). The Duodecimal Bulletin. 4X [59] (2).
13. ^ Andrews, Frank Emerson (1935). New Numbers: How Acceptance of a Duodecimal (12) Base Would Simplify Mathematics. p. 52.
14. ^ Pitman, Isaac (1947). "A Reckoning Reform [reprint from 1857]" (PDF). The Duodecimal Bulletin. 3 (2).
15. ^ a b c "Mo for Megro" (PDF). The Duodecimal Bulletin. 1 (1). 1945.
16. ^ "Annual Meeting of 1973 and Meeting of the Board" (PDF). The Duodecimal Bulletin. 25 [29] (1). 1974.
17. ^ De Vlieger, Michael (2008). "Going Classic" (PDF). The Duodecimal Bulletin. 49 [57] (2).
18. ^ a b Zirkel, Gene (2010). "How Do You Pronounce Dozenals?" (PDF). The Duodecimal Bulletin. 4E [59] (2).
19. ^ Karl Pentzlin (2013-03-30). "Proposal to encode Duodecimal Digit Forms in the UCS" (PDF). ISO/IEC JTC1/SC2/WG2, Document N4399. Retrieved 2016-05-30.
20. ^ "The Unicode Standard, Version 8.0: Number Forms" (PDF). Unicode Consortium. Retrieved 2016-05-30.
21. ^ Scott Pakin (2009). "The Comprehensive LATEX Symbol List" (PDF). Retrieved 2016-05-30.
22. ^ http://www.dozenal.org/articles/DSA-DozenalFAQs.pdf
23. ^ Carroll, Lee (1995). Kryon—Alchemy of the Human Spirit. The Kryon Writings, Inc. ISBN 0-9636304-8-2.
24. ^ "Little Twelvetoes"
25. ^ Pendlebury, Tom (May 2011). "TGM. A coherent dozenal metrology based on Time, Gravity and Mass" (PDF). The Dozenal Society of Great Britain.
26. ^ Suga, Takashi (2002). "Proposal for the Universal Unit System".