67 Pa. Code § 107.4
The following words and terms, when used in this chapter, have the following meanings, unless the context clearly indicates otherwise:
Basic plane-A plane through the centers of the right and left external ear openings and the lower edge of the eye sockets, as shown in Figure 1 of Appendix A, of a reference headform, as shown in Figure 2 of Appendix A or test headform.
Helmet positioning index-The distance in inches, as specified by the manufacturer, from the lowest point of the brow opening at the lateral midpoint of the helmet to the basic plane of a reference headform, when the helmet is firmly and properly positioned on the reference headform.
Midsagittal plane-A longitudinal plane through the apex of a reference headform or test headform that is perpendicular to the basic plane, as shown in Figure 3 of Appendix A.
Reference headform-A measuring device contoured to the dimensions of one of the four headforms described in Appendix A of this chapter with surface markings indicating the locations of the basic, midsagittal, and reference planes, and the centers of the external ear openings.
Reference plane-A plane above and parallel to the basic plane on a reference headform or test headform, as shown in Figure 2 of Appendix A, at the distance indicated in the Appendix A.
Retention system-The complete assembly by which the helmet is retained in position on the head during use.
Test headform-A test device contoured to the dimensions of one of the four reference headforms described in Appendix A for all surface areas that contact the helmet, with surface markings indicating the locations of the basic, midsagittal and reference planes.
67 Pa. Code § 107.4