We make an effort to align the pictures so that the stereo view will appear when the viewer is centered relative to the picture. However, due to production tolerances, there are in practice slight deviations. Here is the recommended procedure for viewing StereoPrints:
Adjust the viewing distance to approximately 50cm,
Holding the picture with your both hands, center your head with respect to it,
You should see a clear stereoscopic view over the whole picture area. If this is not the case, move your head slightly to the left or the right direction, until the stereo view appears.