An index of Bifacial Thinning Flakes (BTF), also known as a Flake of Bifacial Retouch, was developed for this project. This index is defined for complete flakes that have measures for both medial width and thickness. Additional characteristics of BTF that occur in relatively low frequencies, such as platform lipping, were not incorporated in this index (Sullivan and Rozen 1985:758).

In the course of lab work, twenty-three flakes were noted that were "possible thinning flakes" and these were used to assess the BTF index described above. Using the BTF index, 18 of the 23 flakes (78%) flagged as possible BTF were 7 or greater on the BTF index.

Being a general measure, a cutoff of 7 or larger is used to identify "possible BTF" in the following analyses.

When rotations > 0 and Cortex = 10%, BTF =

This index was applied to general collections in the analyses presented in Chapters 6 and 7.