A = line drawn at the level of the maxillary sinus floor;
B = line drawn at the level of the most apical part of the residual alveolar bone wall;
C = line drawn at the level of the most coronal aspect of the residual alveolar bone wall;
D = line drawn at the vestibular aspect of the residual alveolar bone wall;
E = line drawn at the lingual/palatal aspect of the residual alveolar bone wall;
V-VR = vertical;
HR-H1 = horizontal/apical;
HR-H2 = horizontal/coronal.