Formalizing Zebra Tapes as Metrological Artefacts in Optical Rotation Measurements

Zebra tapes (alternating reflective/absorbent sectors printed or applied on adhesive sheets) are widely adopted as low-cost optical references for rotational measurements (speed, rpm counting and phase marking). While counting nominal sectors relies on a deterministic mapping between detected transitions and revolutions, the tape itself is a metrological artifact: imperfections in mounting and geometry can bias the inferred rotational quantity and invalidate the common assumption that transition counting alone guarantees accuracy. This work addresses the resulting gap by modelling how installation-induced defects translate into measurable signal distortions and, ultimately, into uncertainty. We consider the two prevalent layouts, both featuring equally sized reflective and absorbent sectors: the linear tape configuration and the radial arrangement. We show that, while they share most bias mechanisms, the radial configuration introduces additional criticalities. These installation effects modify optical contrast and sector dwell time, producing duty-cycle distortion, amplitude modulation, and edge-time jitter, and may also cause missed or spurious transitions. We then introduce an uncertainty-aware framework that decomposes these contributions and enables a GUM-consistent uncertainty budget when transition loss probability is non-negligible. The approach is validated in a Blade-Tip Timing (BTT) calibration facility, where it is used to derive practical tape-qualification criteria and support traceable reporting of rotational quantities with declared uncertainty.