The CIE standard geometry is shown in the accompanying figure. The measurements will be performed both photometrically and spectrally. While there will be high accuracy and great flexibility, the actual number of samples measured will be limited. Therefore, scales of retroreflection realized by NIST will be disseminated primarily through secondary testing laboratories. CIE angular system for specifying and measuring retroreflectors.
First axis is perpendicular to the plane containing the observation and illumination axes.
Second axis is perpendicular both to the first and reference axes. All axes, angles, and directions of rotation are shown positive.