Refers to the radius of curvature measured in the direction of the line segment b parallel to the sight glass or perpendicular to the line segment through the center of the reflective surface with the instrument specified in Appendix C.
It refers to the radius of curvature measured by the instrument specified in Annex C through the center of the reflecting surface and parallel to or perpendicular to the segment B of the mirror.
Refers to the radius of curvature measured by the instrument specified in Appendix C, passing through the center of the reflecting surface and parallel to the line segment B of the mirror or perpendicular to the line segment.