Document ID: chunk:federal_register_of_legislation:F2015C00542:reg:254:p18
Version: federal_register_of_legislation:F2015C00542
Segment Type: reg
Provision Reference: reg 254 (pt 18/18)
Character Range: 147586–149226

thus obscuring the bright point.

               When a windscreen which exhibits a secondary image is placed between the telescope and the collimator, a second, less bright point appears at a certain distance from the centre of the polar co-ordinate system. The secondary-image separation can be read out as the distance between the points seen through the observation telescope (see Figure 14). (The distance between the dark spot and the bright point at the centre of the polar coordinate system-represents the optical deviation).

              9.3.1.2.3. Expression of results

               The windscreen shall first be examined by a simple scanning technique to establish the area giving the strongest secondary image. That area shall then be examined by the collimation-telescope system at the appropriate angle of incidence. The maximum secondary-image separation shall be measured.

              9.3.1.3. The direction of observation in the horizontal plane shall be maintained approximately normal to the trace of the windscreen in that plane.

              9.3.2. The measurements shall be performed in the zones as defined in paragraph 9.2.2. above according to the vehicle categories.

              9.3.2.1. Vehicle type

               The test shall be repeated if the windscreen is to be fitted to a vehicle of a type in which the forward field of vision differs from that of the vehicle type for which the windscreen has already been approved.

              9.3.3. Indices of difficulty of the secondary characteristics

              9.3.3.1. Nature of the material

Polished (plate) glass  Float glass  Sheet glass