Ahnentafel is a German word meaning Ancestor Table. The ancestors of an individual are numbered so that a father's Ahnentafel number is twice the child's and a mother's number is twice the child's plus one. An individual's child is found by dividing their number by two & ignoring any remainder. This numbering is often used on pedigree charts.
Why I've used it.
I've numbered people on the Ancestor charts to make it easier to identify an individual when following a link from a family page. This is particularly neccessary on the MacLeod chart where the same name can appear several times. The numbers will not show when a page is printed from a recent browser.
The number at the top of a column is the same as the number of individuals in that column.
If an ahnentafel number is converted into binary it shows the path from the subject of the chart to that ancestor. The first digit, always 1, represents the subject, after that 0 represents a father and 1 represents a mother so, for instance, 110 is the subject's mother's father.