A head for math: Master braiders use geometry in creating their intricate hairstyles

Clea White stands back and surveys her customer's features. She eyeballs the contours of the woman's scalp and the thickness of the woman's hair, then she takes the sharp edge of a plastic comb and slices a line through the center of the woman's head.

It is, from all appearances, a simple line - slightly off center at the woman's hairline, over the crown of her head, down to the nape of her neck. White parts the hair quickly, almost intuitively, with no thought of marking, measuring or the subtle elegance of her move.