  In the early fifties, the Belgian Prof. J. de Heinzelin discovered a bone in
the region of a fishermen village called Ishango, at one of the farthest
sources of the Nile, on the border of Congo and Uganda. The Heinzelin's Ishango
bone has notches that seem to form patterns, making it the first tool on which
some logic reasoning seems to have been done. In this paper a new
interpretation is proposed for these patterned notches, based on a detailed
observation of their structure. It can be called the "slide rule"-reading, in
contrast to former "arithmetic game" and "calendar" explanations. Additional
circumstantial evidences are given to support the hypothesis that the Ishango
bone is a primitive mathematical tool using the base 12 and sub-bases 3 and 4.
