Detail design. CAD is central to this stage and SolidWorks (our main CAD system) is used extensively. Here, all the preceding work and knowledge is amassed to develop the design to a production standard. Output is a mixture of 3D model data, documents and drawings that are either fully detailed or a reference drawing accompanying a 3D model. Reference drawings convey only data that cannot be defined or easily visible in a 3D model. This greatly simplifies the design documentation and reduces leadtime. During development, the detail design is kept flexible under a prototype revision system. Once the design goes to production, the revision system changes and is under formal engineering change control.