4.

When the CIL of a retro-reflecting device is measured for an angle β of V = H = 0°, it shall be ascertained whether any mirror effect is produced by slightly turning the device. If there is any such effect, a reading shall be taken with an angle β of V = ±5°, H = 0°. The position adopted shall be that corresponding to the minimum CIL for one of these positions.

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