Section 1203.4 - Definitions(a)Basic plane means an anatomical plane that includes the auditory meatuses (the external ear openings) and the inferior orbital rims (the bottom edges of the eye sockets). The ISO headforms are marked with a plane corresponding to this basic plane (see Figures 1 and 2 of this part).(b)Bicycle helmet means any headgear that either is marketed as, or implied through marketing or promotion to be, a device intended to provide protection from head injuries while riding a bicycle.(c)Comfort or fit padding means resilient lining material used to configure the helmet for a range of different head sizes.(d)Coronal plane is an anatomical plane perpendicular to both the basic and midsagittal planes and containing the midpoint of a line connecting the right and left auditory meatuses. The ISO headforms are marked with a transverse plane corresponding to this coronal plane (see Figures 1 and 2 of this part).(e)Field of vision is the angle of peripheral vision allowed by the helmet when positioned on the reference headform.(f)Helmet positioning index ("HPI") is the vertical distance from the brow of the helmet to the reference plane, when placed on a reference headform. This vertical distance shall be specified by the manufacturer for each size of each model of the manufacturer's helmets, for the appropriate size of headform for each helmet, as described in § 1203.10 .(g)Midsagittal plane is an anatomical plane perpendicular to the basic plane and containing the midpoint of the line connecting the notches of the right and left inferior orbital ridges and the midpoint of the line connecting the superior rims of the right and left auditory meatuses. The ISO headforms are marked with a longitudinal plane corresponding to the midsagittal plane (see Figures 1 and 2 of this part).(h)Modular elastomer programmer ("MEP") is a cylindrical pad, typically consisting of a polyurethane rubber, used as a consistent impact medium for the systems check procedure. The MEP shall be 152 mm (6 in) in diameter, and 25 mm (1 in) thick and shall have a durometer of 60±2 Shore A. The MEP shall be affixed to the top surface of a flat 6.35 mm (1/4 in) thick aluminum plate. See § 1203.17(b)(1) .(i)Preload ballast is a "bean bag" filled with lead shot that is placed on the helmet to secure its position on the headform. The mass of the preload ballast is 5 kg (11 lb).(j)Projection is any part of the helmet, internal or external, that extends beyond the faired surface.(k)Reference headform is a headform used as a measuring device and contoured in the same configuration as one of the test headforms A, E, J, M, and O defined in draft ISO DIS 6220-1983. The reference headform shall include surface markings corresponding to the basic, coronal, midsagittal, and reference planes (see Figures 1 and 2 of this part).(l)Reference plane is a plane marked on the ISO headforms at a specified distance above and parallel to the basic plane (see Figure 3 of this part).(m)Retention system is the complete assembly that secures the helmet in a stable position on the wearer's head.(n)Shield means optional equipment for helmets that is used in place of goggles to protect the eyes.(o)Spherical impactor is an impact fixture used in the instrument system check of § 1203.17(b)(1) to test the impact-attenuation test equipment for precision and accuracy. The spherical impactor shall be a 146 mm (5.75 in) diameter aluminum sphere mounted on the ball-arm connector of the drop assembly. The total mass of the spherical-impactor drop assembly shall be 5.0±0.1 kg (11.0±0.22 lb).(p)Test headform is a solid model in the shape of a human head of sizes A, E, J, M, and O as defined in draft ISO/DIS 6220-1983. Headforms used for the impact-attenuation test shall be constructed of low-resonance K-1A magnesium alloy. The test headforms shall include surface markings corresponding to the basic, coronal, midsagittal, and reference planes (see Figure 2 of this part).(q)Test region is the area of the helmet, on and above a specified impact test line, that is subject to impact testing.