The dendrogram is a graphical summary of the cluster solution. Cases are listed along the left vertical axis. The horizontal axis shows the distance between clusters when they are joined. Parsing the classification tree to determine the number of clusters is a subjective process. Generally, you begin by looking for "gaps" between joinings along the horizontal axis. Starting from the right, there is a gap between 20 and 25, which splits the automobiles into two clusters. There is another gap from approximately 10 to 15, which suggests 6 clusters.