When slightly tilting the label about a vertical axis, both the
parallactic shift in the 2D/3D area and the exploding microtext (Figure 3) can be readily observed even under relatively diffuse illumination.
Those refinements were soon forthcoming with the discovery, for example, that planetary orbits are elliptical rather than circular, and with the development of such instruments as the telescope, which enabled astronomers to make minute observations that proved the existence of
parallactic shifts that were predicted by Copernicus and his followers.