Functional Size measurement (FSM) methods like NESMA FPA and COSMIC can be done in the standard way, in which the in detail described counting rules and guidelines are applied, but these measurements can also be carried out in an approximate way. The authors, who work for the department of Sizing, Estimating & Control of Sogeti Nederland B.V., have analyzed a large number of projects, measuring them with both the detailed methods and the approximate methods. This paper will describe the accuracy percentages found for the different approximate methods as well as the difference in time spent for the various analysis methods.

The study gives a detailed overview of the differences in accuracy between the methods and the differences in effort needed to perform such measurements. This results in a accuracy/cost tradeoff that can be used by organizations to assess the measurement method that is required for a specific project.

This paper was presented at the Software Measurement European Forum in 2009.