Much of the difficulty people have with estimating methods results from using
data from one group to plan work by another person or group.It is important,
therefore,to use data that are relevant to your particular project.This suggests that
you build a size and resouree database for each type of product you develop.If the
proxies you select are not suitable for some kinds of work, examine your data to identify
more suitable proxies. After writing several programs,you should have enough data to identify
useful proxies.