Landmark which is immune to surface deposition and resorption:
Arcial growth of mandible: 

Proposed by Ricketts.
The advantage was that the arc of growth can be constructed for every individual depending on the length of the core of the mandible.
In order to locate the central core, which is immune to surface deposition and resorption, he introduced 2 landmarks - Xi point and Eva point on the mandibular ramus.
Xi Point: Represents geometric centre of ramus.
Eva point: In dried mandible, the stress lines run on the medial aspect parallel to the external oblique ridge and ascend up the ramus. The stress lines fork into two at a  particular point that was named as Eva point.

Ref: Shreedhar Premkumar 1st edition P:199
Xi point and Eva point
Point A and Point B
Porion and Basion
Pogonion and Gnathion