As an example of green performance indicators that characterize the greenness
of each stage in the software engineering process, Mahmoud . suggest performance
or CPU usage. The identified energy usages should be mapped to the
source code to optimize the affected algorithms. Afterwards it is decided whether
even (small) changes in requirements are necessary in order to optimize energy
usage. In fact, this means that the process may step back to Requirements in order
to add missing requirements, correct misunderstandings during the Requirement
phase and in this way optimize the product. They argue that this step back is
acceptable if it results in less severe mistakes. If only changes to the source code
are necessary, these are directly implemented within this phase without stepping
back.