This column is the eighth in a series about estimating. If you are wondering if this series will ever end, hang in, it is almost over. The next two columns conclude the method discussion, and then there is one column on the results engineers have obtained by using the PROBE method in practice.
If you are new to this series of columns on Estimating with Objects, the first was in the July 1996 Object Currents issue. The prior columns in this series gave an overview of estimating and defined some of the steps in making size and resource estimates. If you have not read these earlier columns, you should look at them first to understand the context for this discussion and to see how these various estimating topics relate. To repeat what I have said in previous columns, the estimating method described here is called PROBE. If you want to quickly learn more about PROBE, you should read my book A Discipline for Software Engineering, from Addison Wesley. This book introduces the Personal Software Process (PSP)SM, which is an orderly and defined way for software engineers to do their work.
This column continues the discussion of how to make software estimates. To make a project plan, you need a resource estimate and, to estimate resources, you need to estimate the size of the product you plan to build. Also, to make a good size estimate, you need historical data on the sizes of the programs you have previously written. This and the previous columns describe how to gather these data and how to use them to make the size and resource estimates. In this column, we talk about how you can make accurate estimates and how to judge the accuracy of the estimates you have made.