Michael Eytzinger published a systematic listing of all ancestor of the French king, Henry III, in 1590. Eytzinger developed a system of numbering ancestors that was called Ahnentafel. Also known as the Eytzinger Method, Sosa Method, and Sosa-Stradonitz Method, Ahnentafel 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:
Before Ahnentafel, for centuries royal families had been creating simplified surname charts to clarify who next inherits the throne. Check out a sample of this style in the family chart of Henry VIII of England that included only the ancestors of those who counted enough to be included.
The general description of the Ahnentafel System at the top of the page, and the sample generic chart on the left above is adapted from Wikipedia: Genealogical Numbering Systems. The sample Higdon chart on the right is adapted from the genealogical register report starting on page 263 of Descendants of John Higdon and Millicent 1657-1998, by Gena Lee Theiss.
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