2.1. Survey of Past Mineral Prices and Generation of Cumulative Relative Frequency CurvesTo investigate the variations in mineral prices, data on mineral price of the past over a long period are collected, and statistics such as maximum values, minimum values, and the means of the collected data are obtained using statistical analysis. Using the results of statistical analysis, the class width required for creating cumulative relative frequency curves of mineral prices can be calculated (see Equation (1)). In general, the number of classes is set as between 10 and 20,