The results of the empirical study based on an AR Landolt C vision were examined to compare real and virtual visibility as a function of stimulus size on an HMD (e.g. MS HoloLens 2). A counterbalanced within-subject-design study with n = 32 probands was conducted. The results show on one hand a visibility loss between real and immersive systems by the same size of representation. On the other hand, a transfer function can be derived to ensure comparable visibility between the systems. This transfer function can be used to compensate for the visibility loss as a design guideline for immersive applications. In approximation, the Weber-Fechner's relation can be applied on AR visibility versus size of stimuli.