Translations:Basic Part Design Tutorial 019/6/en

We will follow some of the techniques described in Advice for creating stable models:
 * We will use a master sketch.
 * Named constraints will be used to hold dimensions that can be referenced later in the model construction. For instance, to change the model width from 53 mm, as in the technical drawing, to 55 mm we need only modify the Length value of the appropriate named constraint in the master sketch and the whole model will modify accordingly. This is parametric design in action.
 * External geometries are potentially subject to the Topological Naming Problem. We will use them only when strictly necessary and will attempt to reference to the most stable elements available. Referencing edges and vertices of sketches is normally more stable than referencing edges and vertices of generated solid geometry.