Just reemphasizing some remarks made by others: 1. It is excellent general policy to create geometry using the dimensions which should control a part and will eventually appear on the drawing. A very basic example of this is certainly hole location. If a hole is to be controlled, drawn, and machined with refernce to side surfaces, it should be created that way; if it is to be located relative to the center of the part, it should be created that way. 2. However, an absolute policy of this sort does not take into account the real-world complexity of the modelling environment proviced by the CADD tools or the complexity of geometry development itself. There are numerous times when the efficient, sensible method of geometry creation will not use the dimensions which will ultimately be used for drawings and manufacturing control. This occurs all the time. Just one simple example. You are designing a thin-walled molded part where the most efficient, sensible tool to use is Shell, even though you are going to control the geometry by some internal dimension created as a result of the Shell. You will have to Create that dimension in the Drawing. You might be able to "stand on your head" to create the geometry based on the dimension in question, but if it's going to create a much more complicated Model Tree and be much more tedious to create, then the tail wags the dog. Common sense is required.