The best way to describe a Direct Manipulation interface is by example. Suppose we have a set of data to be analyzed with the numbers stored in matrix form. Their source and meaning are not important for this example: The numbers could be the output of a spreadsheet, a matrix of numerical values from the computations of a conventional programming language, or the results of an experiment. Our goal is to analyze the numbers, to see what relations exist among the rows and columns of the matrix. The matrix of numbers is represented on a computer display screen by an icon.