b).

Figure 6.3a,b: These histograms demonstrates several features of histo. The top histogram (a) shows the distribution of a log-transformed data set (Au - gold). The height of individual bars represents the percentage of all the data samples falling within the given log-value range. The black dashed line in the center of the graph identify the mean of the log-values. The shaded bars in the background show 1, 2, and 3 standard deviation widths from the data set log-mean. This histogram was also plotted using a portrait orientation. The bottom histograms (b) show how two data sets can be displayed on the same graph.