The covariance is similar to the correlation coefficient in that it measures the relationship between a pair of variables. A dendrogram is a 'tree-like' diagram that summaries the process of clustering. Similar cases are joined by links whose position in the diagram is determined by the level of similarity between the cases. The distance between two objects a measure of the interval between them. It is important to understand that distances are not always measured by rulers, or their equivalent.
Measurements of distance are also related to measures of similarity and dissimilarity.
A realistic description of an eigen value demands a sound knowledge of linear algebra. Eigen values are also known as latent variables. Each eigen value has an associated eigen vector. An eigen value gives us the length of an axis, the eigen vector determines its orientation in space. The values in an eigen vector are not unique because any coordinates that described the same orientation would be acceptable.