Driving Dimensions plug-ins allow you to modify any 3D geometry easily. Just add linear, radial or angular dimension between geometric elements of your model (faces, edges, vertices) and type in a desired value: your geometry will be automatically arranged. Moreover, all dimensions, which were set previously, are taking into account when you add a new dimension. It allows you to specify desired behavior when a particular dimension is changed.
August, Google SketchUp Help Group: