Intermediate COCOMO introduces 15 cost drivers divided into 4 groups that account for aspects beyond source lines of code. These subjective ratings are multiplied to determine the effort adjustment factor. It can be used early for rough estimates or later at the component level for more accuracy. COCOMO II improves on the original by basing estimates on an evolving database of past projects rather than just expert judgment. It has models for three stages and estimates costs and schedules for each. While useful, the models have shortcomings like treating all parts of a system equally and not accounting for all external factors.