Chapter 9 315 device, which provides distance information in the z-direction. The distance data is obtained by triangulation of the reflecting red laser beam from the surface of the measured object, in this case hair. Since hair fiber assemblies do not have a continuous solid surface, each z-dimension reading is obtained as an average of measurements obtained from multiple reflections corresponding to fibers at various depths below the outermost hair surface. The utility of this technique lies in its ability to measure volume of hair tresses prepared from straight, curly, or frizzy hair and to monitor the affects of cosmetic treatments such as washing, conditioning, dyeing, etc. In addition, strategies may be employed to monitor the volume of retention of styling polymers when subjected to external stresses, such as high humidity curl retention, physical forces, etc. An example of a straight and frizzy hair tress are provided in Figure 9 to illustrate the volume difference between these two types of hair. Strategies looking forward: Several advanced technology areas offer promise for the analysis of hair volume in the future. To summarize, these are listed below: Figure 9. Images of (a) straight dark brown hair and (b) frizzy dark brown hair alongside three-dimensional plots obtained from experiments carried out with a laser stereometer