The goal of each iteration is an increase in functionality at a constant high quality.

Before an iteration is started, the increase in functionality and the timeline is well defined.

Each iteration is made available to a closed user group. They verify the new functionality. Feedback is integrated within the next iteration.

With such an approach, the customer can constantley measure and verify the progress. Risks are minimized due to the fact that the software must be running at the end of each iteration.