Physical devices for facilitating wearable virtual and/or augmented reality (VR/AR) typically employ stacks containing multiple parallel plates. The parallel plates within the stack may have features and coatings applied to their surfaces to act as waveguides such that, when the device is placed in front of a user's eye, light information from the device periphery is carried and redirected to the eye to produce data or image overlays without blocking normal vision. In some cases, the stacks employ many plates arranged in parallel where each plate guides a different color of light (e.g., red, green and blue). To maintain high quality images, it can be important to achieve good parallelism between plates, to ensure certain surfaces have a desired flatness, and to maintain specific separation distances between the plates during manufacturing, among other factors. The measurement of such parameters can be difficult, however, due to the influence of undesired light reflected from surfaces or features within the stack.
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