air traffic control (AERA) program. The reason the V is so powerful comes from the Hughes culture of coupling all text and analysis to multi dimensional images. It was the foundation of Sequential Thematic Organization of Publications (STOP) created by Hughes in 1963 and used until Hughes was divested by the Howard Hughes Medical Institute in 1985. The US Department of Defense puts the systems engineering process interactions into a V-model relationship. It has now found widespread application in commercial as well as defense programs. Its primary use is in project management and throughout the project lifecycle. One fundamental characteristic of the US V-model is that time and maturity move from left to right and one cannot move back in time. All iteration is along a vertical line to higher or lower levels in the system hierarchy, as shown in the figure. This has proven to be an important aspect of the model. The expansion of the model to a dual-Vee concept is treated in reference. As the V-model is publicly available many companies also use it. In project management it is a method comparable to PRINCE2 and describes methods for project management as well as methods for system development. The V-model, while rigid in process, can be very flexible in application, especially as it pertains to the scope outside of the realm of the System Development Lifecycle normal parameters. Advantages These are the advantages V-model offers in front of other systems development models: The users of the V-model participate in the development and maintenance of the V-model. A change control board publicly maintains the V-model. The change control board meets anywhere from every day to weekly and processes all change requests received during system development and test. The V-model provides concrete assistance on how to implement an activity and its work steps, defining explicitly the events needed to complete a work step: each activity schema contains instructions, recommendations and detailed explanations of the activity. Limits The following aspects are not covered by the V-model, they must be regulated in addition, or the V-model must be adapted accordingly: The placing of contracts for services is not regulated. The organization and execution of operation, maintenance, repair and disposal of the system are not covered by the V-model. However, planning and preparation of a concept for these tasks are regulated in the V-model. The V-model addresses software development within a project rather