What is a "numeric digit"?

Question

I'm reading a technical documentation so every quirky detail, that a normal human being easily realizes to be a typo or just a less well chosen formulation, can, in fact, be a profound base for a concept and can fundamentally affect the future design.

In the said document I can find the term "numeric digit". What is this? Also, what is it not?

In my mind a digit is a character in the set of "0123456789", while something numeric is a a set of characters consisting of characters in the set of "0123456789" (yes, it's the same set).

Perhaps we can define the term in question by exclusion from all the other possible cases' definition. So what would be a good example of the following?

1. a non-numeric digit
2. a numeric non-digit
3. a non-numeric non-digit

My guestimation is this.

1. NST, unless we switch the base (which is too mathematical).
2. NST, unless we declare a string of a digit (which is too programmatic).
3. Anything sans digits (which is a superfluous tautology).

Answer 1

It's just a number, 0-9, as you said. Use of the word "numeric" is just to specify 0-9 as opposed to, say, your thumb.

Answer 2

Common Digits

Although it was not always this way, at one point in the history of the Unicode Standard, they made explicit that a digit was only usable for a base-10 numeric character used to compose big-endian numbers. These digits all have a numeric value ranging from 0 to 9.

In the Unicode character properties, any code point with the general category of Decimal Number also has the Digit character property. In other words, digit=Yes is just an alias for General Category=Decimal Number, or in fact for gc=Nd.

For example, here are your basic Script=Common digits, along with their general categories and numeric values:

U+0030 ‭ 0  GC=Nd      0=NV  SC=Common       DIGIT ZERO
U+0031 ‭ 1  GC=Nd      1=NV  SC=Common       DIGIT ONE
U+0032 ‭ 2  GC=Nd      2=NV  SC=Common       DIGIT TWO
U+0033 ‭ 3  GC=Nd      3=NV  SC=Common       DIGIT THREE
U+0034 ‭ 4  GC=Nd      4=NV  SC=Common       DIGIT FOUR
U+0035 ‭ 5  GC=Nd      5=NV  SC=Common       DIGIT FIVE
U+0036 ‭ 6  GC=Nd      6=NV  SC=Common       DIGIT SIX
U+0037 ‭ 7  GC=Nd      7=NV  SC=Common       DIGIT SEVEN
U+0038 ‭ 8  GC=Nd      8=NV  SC=Common       DIGIT EIGHT
U+0039 ‭ 9  GC=Nd      9=NV  SC=Common       DIGIT NINE

Therefore, there is no such thing as a “non-numeric digit” as far as Unicode is concerned.

Common Non-digit Numbers

On the other hand, there are certainly numbers that do not count as decimal numbers, and hence, as digits. Superscripts and vulgar fractions are considered Other Numbers (gc=No) for example:

U+00B2 ‭ ²  GC=No      2=NV  SC=Common       SUPERSCRIPT TWO
U+00B3 ‭ ³  GC=No      3=NV  SC=Common       SUPERSCRIPT THREE
U+00B9 ‭ ¹  GC=No      1=NV  SC=Common       SUPERSCRIPT ONE
U+00BC ‭ ¼  GC=No    1/4=NV  SC=Common       VULGAR FRACTION ONE QUARTER
U+00BD ‭ ½  GC=No    1/2=NV  SC=Common       VULGAR FRACTION ONE HALF
U+00BE ‭ ¾  GC=No    3/4=NV  SC=Common       VULGAR FRACTION THREE QUARTERS

We also have the interesting case of the “letter numbers”, gc=Nl, which includes such things as Roman Numeral. These are considered numbers not letters, but they are not digits because they are not of use in base-10 composition:

U+2160 ‭ Ⅰ  GC=Nl      1=NV  SC=Latin        ROMAN NUMERAL ONE
U+2161 ‭ Ⅱ  GC=Nl      2=NV  SC=Latin        ROMAN NUMERAL TWO
U+2162 ‭ Ⅲ  GC=Nl      3=NV  SC=Latin        ROMAN NUMERAL THREE
U+2163 ‭ Ⅳ  GC=Nl      4=NV  SC=Latin        ROMAN NUMERAL FOUR
U+2164 ‭ Ⅴ  GC=Nl      5=NV  SC=Latin        ROMAN NUMERAL FIVE
U+2165 ‭ Ⅵ  GC=Nl      6=NV  SC=Latin        ROMAN NUMERAL SIX
U+2166 ‭ Ⅶ  GC=Nl      7=NV  SC=Latin        ROMAN NUMERAL SEVEN
U+2167 ‭ Ⅷ  GC=Nl      8=NV  SC=Latin        ROMAN NUMERAL EIGHT
U+2168 ‭ Ⅸ  GC=Nl      9=NV  SC=Latin        ROMAN NUMERAL NINE
U+2169 ‭ Ⅹ  GC=Nl     10=NV  SC=Latin        ROMAN NUMERAL TEN
U+216A ‭ Ⅺ  GC=Nl     11=NV  SC=Latin        ROMAN NUMERAL ELEVEN
U+216B ‭ Ⅻ  GC=Nl     12=NV  SC=Latin        ROMAN NUMERAL TWELVE
U+216C ‭ Ⅼ  GC=Nl     50=NV  SC=Latin        ROMAN NUMERAL FIFTY
U+216D ‭ Ⅽ  GC=Nl    100=NV  SC=Latin        ROMAN NUMERAL ONE HUNDRED
U+216E ‭ Ⅾ  GC=Nl    500=NV  SC=Latin        ROMAN NUMERAL FIVE HUNDRED
U+216F ‭ Ⅿ  GC=Nl   1000=NV  SC=Latin        ROMAN NUMERAL ONE THOUSAND

Uncommon Digits

There are many other digits than the basic ten from the Common script, however. For example:

U+0660 ‭ ٠  GC=Nd      0=NV  SC=Common       ARABIC-INDIC DIGIT ZERO
U+0661 ‭ ١  GC=Nd      1=NV  SC=Common       ARABIC-INDIC DIGIT ONE
U+0662 ‭ ٢  GC=Nd      2=NV  SC=Common       ARABIC-INDIC DIGIT TWO
U+0663 ‭ ٣  GC=Nd      3=NV  SC=Common       ARABIC-INDIC DIGIT THREE
U+07C0 ‭ ߀  GC=Nd      0=NV  SC=Nko          NKO DIGIT ZERO
U+07C1 ‭ ߁  GC=Nd      1=NV  SC=Nko          NKO DIGIT ONE
U+07C2 ‭ ߂  GC=Nd      2=NV  SC=Nko          NKO DIGIT TWO
U+07C3 ‭ ߃  GC=Nd      3=NV  SC=Nko          NKO DIGIT THREE
U+0966 ‭ ०  GC=Nd      0=NV  SC=Devanagari   DEVANAGARI DIGIT ZERO
U+0967 ‭ १  GC=Nd      1=NV  SC=Devanagari   DEVANAGARI DIGIT ONE
U+0968 ‭ २  GC=Nd      2=NV  SC=Devanagari   DEVANAGARI DIGIT TWO
U+0969 ‭ ३  GC=Nd      3=NV  SC=Devanagari   DEVANAGARI DIGIT THREE
U+096F ‭ ९  GC=Nd      9=NV  SC=Devanagari   DEVANAGARI DIGIT NINE
U+09E6 ‭ ০  GC=Nd      0=NV  SC=Bengali      BENGALI DIGIT ZERO
U+09E7 ‭ ১  GC=Nd      1=NV  SC=Bengali      BENGALI DIGIT ONE
U+09E8 ‭ ২  GC=Nd      2=NV  SC=Bengali      BENGALI DIGIT TWO
U+09E9 ‭ ৩  GC=Nd      3=NV  SC=Bengali      BENGALI DIGIT THREE

and many more besides. Those are all digits: note the GC=Nd. They just aren’t in the Common script.

Uncommon Non-Digit Numbers

Here are some other numbers that aren’t in the common script and which are not digits. Some have interesting numeric values, as you see.

U+09F4 ‭ ৴  GC=No   1/16=NV  SC=Bengali      BENGALI CURRENCY NUMERATOR ONE
U+09F5 ‭ ৵  GC=No    1/8=NV  SC=Bengali      BENGALI CURRENCY NUMERATOR TWO
U+09F6 ‭ ৶  GC=No   3/16=NV  SC=Bengali      BENGALI CURRENCY NUMERATOR THREE
U+09F7 ‭ ৷  GC=No    1/4=NV  SC=Bengali      BENGALI CURRENCY NUMERATOR FOUR
U+09F8 ‭ ৸  GC=No    3/4=NV  SC=Bengali      BENGALI CURRENCY NUMERATOR ONE LESS THAN THE DENOMINATOR
U+09F9 ‭ ৹  GC=No     16=NV  SC=Bengali      BENGALI CURRENCY DENOMINATOR SIXTEEN
U+0D70 ‭ ൰  GC=No     10=NV  SC=Malayalam    MALAYALAM NUMBER TEN
U+0D71 ‭ ൱  GC=No    100=NV  SC=Malayalam    MALAYALAM NUMBER ONE HUNDRED
U+0D72 ‭ ൲  GC=No   1000=NV  SC=Malayalam    MALAYALAM NUMBER ONE THOUSAND
U+0D73 ‭ ൳  GC=No    1/4=NV  SC=Malayalam    MALAYALAM FRACTION ONE QUARTER
U+0D74 ‭ ൴  GC=No    1/2=NV  SC=Malayalam    MALAYALAM FRACTION ONE HALF
U+0D75 ‭ ൵  GC=No    3/4=NV  SC=Malayalam    MALAYALAM FRACTION THREE QUARTERS
U+0F2A ‭ ༪  GC=No    1/2=NV  SC=Tibetan      TIBETAN DIGIT HALF ONE
U+0F2B ‭ ༫  GC=No    3/2=NV  SC=Tibetan      TIBETAN DIGIT HALF TWO
U+0F2C ‭ ༬  GC=No    5/2=NV  SC=Tibetan      TIBETAN DIGIT HALF THREE
U+0F2D ‭ ༭  GC=No    7/2=NV  SC=Tibetan      TIBETAN DIGIT HALF FOUR
U+0F2E ‭ ༮  GC=No    9/2=NV  SC=Tibetan      TIBETAN DIGIT HALF FIVE
U+0F2F ‭ ༯  GC=No   11/2=NV  SC=Tibetan      TIBETAN DIGIT HALF SIX
U+0F30 ‭ ༰  GC=No   13/2=NV  SC=Tibetan      TIBETAN DIGIT HALF SEVEN
U+0F31 ‭ ༱  GC=No   15/2=NV  SC=Tibetan      TIBETAN DIGIT HALF EIGHT
U+0F32 ‭ ༲  GC=No   17/2=NV  SC=Tibetan      TIBETAN DIGIT HALF NINE
U+0F33 ‭ ༳  GC=No   -1/2=NV  SC=Tibetan      TIBETAN DIGIT HALF ZERO
U+2180 ‭ ↀ  GC=Nl   1000=NV  SC=Latin        ROMAN NUMERAL ONE THOUSAND C D
U+2181 ‭ ↁ  GC=Nl   5000=NV  SC=Latin        ROMAN NUMERAL FIVE THOUSAND
U+2182 ‭ ↂ  GC=Nl  10000=NV  SC=Latin        ROMAN NUMERAL TEN THOUSAND
U+2185 ‭ ↅ  GC=Nl      6=NV  SC=Latin        ROMAN NUMERAL SIX LATE FORM
U+2186 ‭ ↆ  GC=Nl     50=NV  SC=Latin        ROMAN NUMERAL FIFTY EARLY FORM
U+2187 ‭ ↇ  GC=Nl  50000=NV  SC=Latin        ROMAN NUMERAL FIFTY THOUSAND
U+2188 ‭ ↈ  GC=Nl 100000=NV  SC=Latin        ROMAN NUMERAL ONE HUNDRED THOUSAND
U+2CFD ‭ ⳽  GC=No    1/2=NV  SC=Coptic       COPTIC FRACTION ONE HALF

Into the Astral Planes

And those are only examples are numbers in the Basic Multilingual Plane, which makes up only ¹⁄₁₇ of the available code points in Unicode. Venturing into the astral planes, we find such delights as these:

U+10140 ‭ 𐅀  GC=Nl    1/4=NV  SC=Greek        GREEK ACROPHONIC ATTIC ONE QUARTER
U+10141 ‭ 𐅁  GC=Nl    1/2=NV  SC=Greek        GREEK ACROPHONIC ATTIC ONE HALF
U+10142 ‭ 𐅂  GC=Nl      1=NV  SC=Greek        GREEK ACROPHONIC ATTIC ONE DRACHMA
U+10143 ‭ 𐅃  GC=Nl      5=NV  SC=Greek        GREEK ACROPHONIC ATTIC FIVE
U+10144 ‭ 𐅄  GC=Nl     50=NV  SC=Greek        GREEK ACROPHONIC ATTIC FIFTY
U+10145 ‭ 𐅅  GC=Nl    500=NV  SC=Greek        GREEK ACROPHONIC ATTIC FIVE HUNDRED
U+10146 ‭ 𐅆  GC=Nl   5000=NV  SC=Greek        GREEK ACROPHONIC ATTIC FIVE THOUSAND
U+10147 ‭ 𐅇  GC=Nl  50000=NV  SC=Greek        GREEK ACROPHONIC ATTIC FIFTY THOUSAND
U+10175 ‭ 𐅵  GC=No    1/2=NV  SC=Greek        GREEK ONE HALF SIGN
U+10176 ‭ 𐅶  GC=No    1/2=NV  SC=Greek        GREEK ONE HALF SIGN ALTERNATE FORM
U+10177 ‭ 𐅷  GC=No    2/3=NV  SC=Greek        GREEK TWO THIRDS SIGN
U+10178 ‭ 𐅸  GC=No    3/4=NV  SC=Greek        GREEK THREE QUARTERS SIGN
U+1018A ‭ 𐆊  GC=No      0=NV  SC=Greek        GREEK ZERO SIGN
U+10320 ‭ 𐌠  GC=No      1=NV  SC=Old_Italic   OLD ITALIC NUMERAL ONE
U+10321 ‭ 𐌡  GC=No      5=NV  SC=Old_Italic   OLD ITALIC NUMERAL FIVE
U+10322 ‭ 𐌢  GC=No     10=NV  SC=Old_Italic   OLD ITALIC NUMERAL TEN
U+10323 ‭ 𐌣  GC=No     50=NV  SC=Old_Italic   OLD ITALIC NUMERAL FIFTY
U+10341 ‭ 𐍁  GC=Nl     90=NV  SC=Gothic       GOTHIC LETTER NINETY
U+1034A ‭ 𐍊  GC=Nl    900=NV  SC=Gothic       GOTHIC LETTER NINE HUNDRED
U+10E78 ‭ 𐹸  GC=No    700=NV  SC=Arabic       RUMI NUMBER SEVEN HUNDRED
U+10E79 ‭ 𐹹  GC=No    800=NV  SC=Arabic       RUMI NUMBER EIGHT HUNDRED
U+10E7A ‭ 𐹺  GC=No    900=NV  SC=Arabic       RUMI NUMBER NINE HUNDRED
U+10E7B ‭ 𐹻  GC=No    1/2=NV  SC=Arabic       RUMI FRACTION ONE HALF
U+10E7C ‭ 𐹼  GC=No    1/4=NV  SC=Arabic       RUMI FRACTION ONE QUARTER
U+10E7D ‭ 𐹽  GC=No    1/3=NV  SC=Arabic       RUMI FRACTION ONE THIRD
U+10E7E ‭ 𐹾  GC=No    2/3=NV  SC=Arabic       RUMI FRACTION TWO THIRDS
 ONE HUNDRED
U+11065 ‭ 𑁥  GC=No   1000=NV  SC=Brahmi       BRAHMI NUMBER ONE THOUSAND
U+12400 ‭ 𒐀  GC=Nl      2=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN TWO ASH
U+12401 ‭ 𒐁  GC=Nl      3=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN THREE ASH
U+12402 ‭ 𒐂  GC=Nl      4=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN FOUR ASH
U+12403 ‭ 𒐃  GC=Nl      5=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN FIVE ASH
U+12404 ‭ 𒐄  GC=Nl      6=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN SIX ASH
U+12458 ‭ 𒑘  GC=Nl      1=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN ONE ESHE3
U+12459 ‭ 𒑙  GC=Nl      2=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN TWO ESHE3
U+1245A ‭ 𒑚  GC=Nl    1/3=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN ONE THIRD DISH
U+1245B ‭ 𒑛  GC=Nl    2/3=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN TWO THIRDS DISH
U+1245C ‭ 𒑜  GC=Nl    5/6=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN FIVE SIXTHS DISH
U+1245D ‭ 𒑝  GC=Nl    1/3=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN ONE THIRD VARIANT FORM A
U+1245E ‭ 𒑞  GC=Nl    2/3=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN TWO THIRDS VARIANT FORM A
U+1245F ‭ 𒑟  GC=Nl    1/8=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN ONE EIGHTH ASH
U+12460 ‭ 𒑠  GC=Nl    1/4=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN ONE QUARTER ASH
U+12461 ‭ 𒑡  GC=Nl    1/6=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN OLD ASSYRIAN ONE SIXTH
U+12462 ‭ 𒑢  GC=Nl    1/4=NV  SC=Cuneiform    CUNEIFORM NUMERIC SIGN OLD ASSYRIAN ONE QUARTER

Aren’t you glad you asked? 😈

Answer 3

If you gave some more specific context (like the subject matter, or some surrounding verbiage), we might be able to give a more targeted answer. For now, given that all we know is that this phrase appears "in a technical document", my strong suspicion is that it's merely an unnecessarily verbose way to say digit.

I don't think disambiguation between numerals and fingers plays into it, though I could change my mind on this depending on the subject of the document.

Answer 4

A numeric digit is the smallest instance of what you call (but inadequately define) as “something numeric”. Your definition is inadequate because it fails to include the phrase “optionally, with an algebraic sign”. (Your definition also presupposes base 10, and we’ll go with that in this answer. For other bases, adjust accordingly.) The standard terminology for “something numeric” is “a numeric literal”. All other literals are called “alphanumeric” literals. The operational distinction between the two is that (normal) arithmetic can be done on the former, but not on the latter. Thus, an arbitrary string of digits is not necessarily a numeric literal - zip codes and telephone numbers (without punctuation) are the classic examples of this. (The reason that we have to specify “normal” arithmetic is that what are called “hash totals” are computed on arbitrary (alphanumeric) data, using the internal numeric codes for characters, as a check on data transmission integrity, much in the same spirit of what are called “check digits” - another case where special numeric computation is done on a string of “non-numeric” digits.)