The arrangement of artifact types in a sequence is based on two simple ideas: first, that products of a given period and place havea distinctive style or design; and second, that changes in each style are gradual, or evolutionary. Gradual changes in design are evident in the history of the automobile(top)and of the prehistoric European axe(above: (1) stone, (2-5) bronze). However, the rate of change (a century for the automobile, millennia for the axe) has to be deduced from absolute dating methods