This paper illustrates how electronic spreadsheet programs, such as Lotus 1-2-3 and Microsoft Excel, can be used for numerical analysis. It begins by considering the nature of spreadsheets with particular reference to their precision and accuracy. It continues with an extended example taken from matrix manipulation which uses both the Jacobi and Gauss-Seidel iterative methods for solving sets of simultaneous equations. The spreadsheet approach allows users to compare the details of how the two methods work. The paper concludes with a restatement of the advantages of spreadsheets for numerical analysis.