Wheel housing check
Parallel gear control

Reference surfaces are those used to define the reference axis.

The reference axis is the one that will be used by the designer (and controller) to define the geometry of the wheel teeth of an individual component.

The reference axis is usually defined so that it coincides with the functional axis, using the mounting surfaces as reference surfaces.

Even so, it will be necessary to define a reference axis and then link the other axes (including the functional axis and...