This standard specifies a method for determining the proportion of true spheres in Glass beads used for reflective marking. The test consists of two procedures: Procedure A and Procedure B, which are applicable to different Glass bead size ranges, respectively. By measuring the roundness of Glass beads, their performance as an inverse reflection medium can be assessed. The test results are crucial to ensure the Optical Properties of the marking material. True sphere proportions that meet the specification requirements enable improved effectiveness and durability of reflective marking.