Horizontal 15-point intensity scale

Interval scale Panelists score the samples in a structured scale, in which each value is separated by a constant interval. The exact intervals vary according to tradition (nine-point hedonic scale, 100-point scale). The psychological error of central tendency , i.e., avoidance of the endpoint scale, is frequently observed in scoring. Alternatively, a nonnumerical or graphical scale can be used, consisting of a horizontal line on which panelists mark a position on the scale the scale is then converted to centimeters for numerical analysis. Anchors are presented along with the experimental samples to illustrate minimum and maximum intensities within the test. Line scales permit fineness of differentiation among responses and are examples of continuous scales. 

In the Steiner Tunnel of ASTM E 84-1981a (cf. Section 3.2.1, Fig. 3.93), flame spreading is measured on a specimen with surface area of 7320 mm x 508 mm. In the horizontal vent pipe of 408 mm dia. at the outlet of the tunnel, changes in the intensity of a vertical light beam are recorded during the test procedure. The area under the intensity vs, time curve for the specimen is divided by that for a red oak specimen and multiplied by 100, to establish a numerical index for comparison of the performance of the material to that of an asbestos-cement board and of red oak, taking these as limit points of an arbitrary centesimal scale (0 and 100, respectively). 

Figure 5 shows the BRDF plot for two randomly polished mirrors. As explained previously, this is a plot of scattered intensity versus angle. The 0° point on the horizontal axis indicates the direction of the specular reflection. All other directions on the plot are relative to this direction (0, — 0j in Fig. 4). The vertical axis is the BRDF scatter (on a logarithmic scale). BRDF is typically plotted on a logarithmic scale because it changes over several orders of magnitude within a few degrees of the specular beam.

---