The different machine categories are represented by squares, and similar to the
mechanic categories, the shades behind each square represent where there can be several
machines within that machine category. The lines and nodes in Figure 1, starting from the
mechanic categories’ node, indicate the different machine categories that each mechanic
category is capable of servicing. Conversely, starting at the machine categories’ node, the
lines show the different mechanic categories that are capable of servicing each machine
category.