Some tools allow you to play with various options easily and quickly. Whenever an estimate is generated, everyone wants to know how close the numbers are to reality. Well, the bottom line is that you won t know exactly until you finish the project and you will have to live with some uncertainty. Naturally, you will want every estimate to be as accurate as possible given the data you have at the time you generate it. Accuracy is an indication of how close something is to reality.
Precision is an indication of how finely something is measured.
For example, a size estimate of 70 to 80 KLOC might be both the most accurate and the most precise estimate you can make at the end of the requirements specification phase of a project. If you simplify your size estimate to 75000 LOC it looks more precise, but in reality it s less accurate. This is where a solid understanding of the relationships between these variables is so important, and where being armed with different project estimates illustrating the tradeoffs is very useful for establishing what the limits are. If you lengthen the schedule, you can generally reduce the overall cost and use fewer people. Sometimes you only have to lengthen the schedule by a few weeks to get a benefit.