Figure 3.04. X-Y transformation to ternary.. When using percentages to plot chemical compositions or other data, the sum of the percentages is always 100%. This means that the percentage of one of the things being plotted can be calculated from the others. Therefore, when there are only three things, such as for a three-component system, there are only two independent percentages and these can be plotted on a graph in two dimensions like the X-Y graph shown in this figure. If the the two axes are drawn 60° apart, rather than 90° apart, all possible combinations of component percentages fall within an equilateral triangle and the percentage of the 3rd thing can be easily read from the diagram. The relationship of a standard cartesian X-Y graph to a ternary diagram is revealed by this figure. Use your mouse to move the slider down and watch the X-Y graph transform into a ternary diagram.