As is well known, the actual objective of the impact tests defined in the standards is to determine the withstand capacity of various materials used for guards. Commonly used for this purpose are steel sheets and transparent plastics for the viewing windows, the latter being of great importance for the safe use of the machine.

The total scatter of the determined impact resistance adds up to numerous individual effects, which can lead to a considerable random measurement error, as described in a separate paper [3]. Only when a model for this measurement error is available can the withstand capacity of the polycarbonate sheets under investigation be determined indirectly from the velocity measurements of the projectile with some "accuracy". This is because the impact resistance of polycarbonate sheets, considered in isolation, also scatters itself to a not inconsiderable extent, as is generally known for plastics.

The total scatter of the determined impact resistance adds up from the individual effects as follows: a) normative tolerance ranges for the impact velocity measurement, b) a limited repeatability in the velocity measurement resulting from a very complex test technique, c) significant deviations in repeat tests for the exact impact conditions and the impact conditions. The overlap of these scatter effects causes an inherent measurement error of the whole measurement apparatus. For this purpose, a distribution function is to be determined (estimated) as a model for the first time using the means of descriptive statistics. The interaction of the scattering effects is assumed to be random and symmetrical. Because of the numerous random individual effects in b) and c), a (first) Gaussian bell curve can be assumed in the sense of the Central Limit Theorem. Thus, it is necessary to determine its characteristic value “mean value” and "standard deviation”.