School mathematics is generally presented as essentially static and subject to only few changes. Likewise, mathematics itself seems to have a cumulative character where all earlier periods and achievements are somehow "preserved" within the modern state of mathematics. The logarithms present a case, which contradicts both convictions. Established as a device for facilitating complicated calculations, they were over centuries, until recently, an indispensable tool for mathematicians, and logarithmic tables constituted therefore a key subject for learning in secondary schools, too. Today, computers and hand-held calculators have entirely substituted this traditional knowledge. The example of a particular German logarithmic table leads not only to revealing studies for determining the author of the table, but moreover to epistemological insights into the nature and development of mathematics and the relation between pure and applied mathematics.