Several genealogical numbering systems have been widely adopted for presenting family trees and pedigree charts in text format. Among the most popular numbering systems are: Ahnentafel (Sosa-Stradonitz Method), and the Register, NGSQ, Henry, d'Aboville, Meurgey de Tupigny, and de Villiers/Pama Systems .

## Ascending numbering systems

### Ahnentafel

Ahnentafel, also known as the Eytzinger Method, Sosa Method, and Sosa-Stradonitz Method, allows for the numbering of ancestors beginning with a descendant. This system allows one to derive an ancestor's number without compiling the list and allows one to derive an ancestor's relationship based on their number.

The number of a person's father is the double of their own number, and the number of a person's mother is the double of their own, plus one. For instance, if the number of John Smith is 10, his father is 20, and his mother is 21.

The first 15 numbers, identifying individuals in 4 generations, are as follows:

```(First Generation)
1  Subject

(Second Generation)
2  Father
3  Mother

(Third Generation)
4  Father's father
5  Father's mother
6  Mother's father
7  Mother's mother

(Fourth Generation)
8  Father's father's father
9  Father's father's mother
10  Father's mother's father
11  Father's mother's mother
12  Mother's father's father
13  Mother's father's mother
14  Mother's mother's father
15  Mother's mother's mother
```

### Ahnentafel with generation

In order to readily have the generation stated for a certain person, the ahnentafel numbering may be preceded by the generation, hence (with more readable alternative):

```(First Generation)
1-1 (01-001)  Subject

(Second Generation)
2-2 (02-002) Father
2-3 (02-003) Mother

(Third Generation)
3-4 (03-004) Father's father
3-5 (03-005) Father's mother
3-6 (03-006) Mother's father
3-7 (03-007) Mother's mother

(Fourth Generation)
4-8 (04-008) Father's father's father
4-9 (04-009) Father's father's mother
4-10 (04-010) Father's mother's father
4-11 (04-011) Father's mother's mother
4-12 (04-012) Mother's father's father
4-13 (04-013) Mother's father's mother
4-14 (04-014) Mother's mother's father
4-15 (04-015) Mother's mother's mother
```

This method's usefulness comes readily into view when applied further back in the generations, e.g., 08-146, is a male preceding the subject by 7 (8-1) generations. This ancestor was the father of a woman (146/2=73) (in the genealogy line of the subject), that was the mother of a man (73/2=36(.5)), further down the line the father of a man (36/2=18), father of a woman (18/2=9), mother of a man (9/2=4(.5)), father of the subject's father (4/2=2). Hence, 08-146, is the subject's father's father's mother's father's father's mother's father ("puh").

### atree

atree or Binary Ahnentafel method uses the same numbering of nodes in the binary ancestors tree as Ahnentafel method, but uses binary numbers instead. For a female in the root the correspondence between binary and atree numbering is straightforward, but for male in the root - the first digit is 1 (i.e. M anyway) - to avoid trimming 0s. The advantage of atree system is easier understanding of the genealogical path (as a path from the root) and binary numbering system is natural for the binary tree.

The first 15 numbers in 4 generations in atree system (note that "M" and "F" represent "male [ancestor]" and "female [ancestor]" respectively, as opposed to "mother" and "father"):

```_  [Placeholder for subject, to be filled with M if subject is male or F if subject is female]
_M  Father
_F  Mother
_MM  Father's father
_MF  Father's mother
_FM  Mother's father
_FF  Mother's mother
_MMM  Father's father's father
_MMF  Father's father's mother
_MFM  Father's mother's father
_MFF  Father's mother's mother
_FMM  Mother's father's father
_FMF  Mother's father's mother
_FFM  Mother's mother's father
_FFF  Mother's mother's mother
```

Explanation of the correspondence between atree IDs and Ahnentafel decimal IDs:

person Ahnentafel format binary format atree (for women) atree (for men)
Subject 1 1 F M
Father 2 10 FM MM
Mother 3 11 FF MF
Father's father 4 100 FMM MMM
Father's mother 5 101 FMF MMF
Mother's father 6 110 FFM MFM
Mother's mother 7 111 FFF MFF

### Surname methods

Genealogical writers sometimes choose to present ancestral lines by carrying back individuals with their spouses or single families generation by generation. The siblings of the individual or individuals studied may or may not be named for each family. This method is most popular in simplified single surname studies, however, allied surnames of major family branches may be carried back as well. In general, numbers are assigned only to the primary individual studied in each generation.[1]

## Descending numbering systems

### Register System

The Register System uses both common numerals (1, 2, 3, 4) and Roman numerals (i, ii, iii, iv). The system is organized by generation, i.e., generations are grouped separately.

The system was created in 1870 for use in the New England Historic and Genealogical Register published by the New England Historic Genealogical Society based in Boston, Massachusetts. Register Style, of which the numbering system is part, is one of two major styles used in the U.S. for compiling descending genealogies. (The other being the NGSQ System.)[2]

```      (–Generation One–)
1 Progenitor
2     i  Child
ii  Child (no progeny)
iii  Child (no progeny)
3    iv  Child
```
```      (–Generation Two–)
2 Child
i  Grandchild (no progeny)
ii  Grandchild (no progeny)
3 Child
4     i  Grandchild
```
```      (–Generation Three–)
4 Grandchild
5     i  Great-grandchild
ii  Great-grandchild (no progeny)
6   iii  Great-grandchild
7    iv  Great-grandchild
```

### NGSQ System

The NGSQ System gets its name from the National Genealogical Society Quarterly published by the National Genealogical Society headquartered in Arlington, Virginia, which uses the method in its articles. It is sometimes called the "Record System" or the "Modified Register System" because it derives from the Register System. The most significant difference between the NGSQ and the Register Systems is in the method of numbering for children who are not carried forward into future generations: The NGSQ System assigns a number to every child, whether or not that child is known to have progeny, and the Register System does not. Other differences between the two systems are mostly stylistic.[1]

```      (–Generation One–)
1 Progenitor
+  2     i  Child
3    ii  Child (no progeny)
4   iii  Child (no progeny)
+  5    iv  Child
```
```      (–Generation Two–)
2 Child
6     i  Grandchild (no progeny)
7    ii  Grandchild (no progeny)
5 Child
+  8     i  Grandchild
```
```      (–Generation Three–)
8 Grandchild
+  9     i  Great-grandchild
10    ii  Great-grandchild (no progeny)
+ 11   iii  Great-grandchild
+ 12    iv  Great-grandchild
```

### Henry System

The Henry System is a descending system created by Reginald Buchanan Henry for a genealogy of the families of the presidents of the United States that he wrote in 1935.[3] It can be organized either by generation or not. The system begins with 1. The oldest child becomes 11, the next child is 12, and so on. The oldest child of 11 is 111, the next 112, and so on. The system allows one to derive an ancestor's relationship based on their number. For example, 621 is the first child of 62, who is the second child of 6, who is the sixth child of his parents.

In the Henry System, when there are more than nine children, X is used for the 10th child, A is used for the 11th child, B is used for the 12th child, and so on. In the Modified Henry System, when there are more than nine children, numbers greater than nine are placed in parentheses.

```Henry		                   Modified Henry
1. Progenitor 		               1. Progenitor
11. Child		                  11. Child
111. Grandchild		              111. Grandchild
1111. Great-grandchild                1111. Great-grandchild
1112. Great-grandchild                1112. Great-grandchild
112. Grandchild		              112. Grandchild
12. Child		                  12. Child
121. Grandchild		              121. Grandchild
1211. Great-grandchild                1211. Great-grandchild
1212. Great-grandchild                1212. Great-grandchild
122. Grandchild		              122. Grandchild
1221. Great-grandchild                1221. Great-grandchild
123. Grandchild		              123. Grandchild
124. Grandchild		              124. Grandchild
125. Grandchild		              125. Grandchild
126. Grandchild		              126. Grandchild
127. Grandchild		              127. Grandchild
128. Grandchild		              128. Grandchild
129. Grandchild		              129. Grandchild
12X. Grandchild		              12(10). Grandchild
```

### d'Aboville System

The d'Aboville System is a descending numbering method developed by Jacques d'Aboville in 1940 that is very similar to the Henry System, widely used in France.[4] It can be organized either by generation or not. It differs from the Henry System in that periods are used to separate the generations and no changes in numbering are needed for families with more than nine children.[5] For example:

```1 Progenitor
1.1 Child
1.1.1 Grandchild
1.1.1.1 Great-grandchild
1.1.1.2 Great-grandchild
1.1.2 Grandchild
1.2 Child
1.2.1 Grandchild
1.2.1.1 Great-grandchild
1.2.1.2 Great-grandchild
1.2.2 Grandchild
1.2.2.1 Great-grandchild
1.2.3 Grandchild
1.2.4 Grandchild
1.2.5 Grandchild
1.2.6 Grandchild
1.2.7 Grandchild
1.2.8 Grandchild
1.2.9 Grandchild
1.2.10 Grandchild
```

### Meurgey de Tupigny System

The Meurgey de Tupigny System is a simple numbering method used for single surname studies and hereditary nobility line studies developed by Jacques Meurgey de Tupigny of the National Archives of France, published in 1953.[6]

Each generation is identified by a Roman numeral (I, II, III, ...), and each child and cousin in the same generation carrying the same surname is identified by an Arabic numeral.[7] The numbering system usually appears on or in conjunction with a pedigree chart. Example:

```I Progenitor
II-1 Child
III-1 Grandchild
IV-1  Great-grandchild
IV-2  Great-grandchild
III-2 Grandchild
III-3 Grandchild
III-4 Grandchild
II-2 Child
III-5 Grandchild
IV-3  Great-grandchild
IV-4  Great-grandchild
IV-5  Great-grandchild
III-6 Grandchild
```

### de Villiers/Pama System

The de Villiers/Pama System gives letters to generations, and then numbers children in birth order. For example:

```a Progenitor
b1 Child
c1 Grandchild
d1 Great-grandchild
d2 Great-grandchild
c2 Grandchild
c3 Grandchild
b2 Child
c1 Grandchild
d1 Great-grandchild
d2 Great-grandchild
d3 Great-grandchild
c2 Grandchild
c3 Grandchild
```

In this system, b2.c3 is the third child of the second child,[8] and is one of the progenitor's grandchildren.

The de Villiers/Pama system is the standard for genealogical works in South Africa. It was developed in the 19th century by Christoffel Coetzee de Villiers and used in his three volume Geslachtregister der Oude Kaapsche Familien (Genealogies of Old Cape Families). The system was refined by Dr. Cornelis (Cor) Pama, one of the founding members of the Genealogical Society of South Africa.[9]

## References

1. ^ a b Curran, Joan Ferris. Numbering Your Genealogy: Sound and Simple Systems. Arlington, Virginia: National Genealogical Society, 1992.
2. ^ Curran, Joan Ferris, Madilyn Coen Crane, and John H. Wray.Numbering Your Genealogy: Basic Systems, Complex Families, and International Kin. Arlington, Virginia: National Genealogical Society, 1999.
3. ^ Henry, Reginald Buchanan. Genealogies of the Families of the Presidents. Rutland, Vermont: The Tuttle Company, 1935.
4. ^ Généalogie-Standard: Les systèmes de numérotation (Numbering Systems)
5. ^ Encyclopedia of Genealogy: d'Aboville Numbers
6. ^ Guide des recherches généalogiques aux Archives Nationales. Paris, 1953 (Bn : 8° L43 119 [1])
7. ^ Standard GenWeb: La numérotation Meurgey de Tupigny
8. ^ Numbering Systems In Genealogy - de Villiers/Pama by Richard A. Pence
9. ^ Genealogical Society of South Africa
Notes