After building this cache I had second thoughts about puting it out. I thought it might be to difficult for people to see and understand. I showed it to one of the local geocaching legends to test it and he had it solved in less than a minute. So here goes nothing.
Persistence of vision traditionally refers to the optical illusion that occurs when visual perception of an object does not cease for some time after the rays of light proceeding from it have ceased to enter the eye. The illusion has also been described as "retinal persistence", "persistence of impressions", simply "persistence" and other variations. According to this definition, the illusion would be the same as, or very similar to positive afterimages.
"Persistence of vision" can also be understood to mean the same as "flicker fusion", the effect that vision seems to persist continuously when the light that enters the eyes is interrupted with short and regular intervals.
Early descriptions of the illusion often attributed the effect purely to imperfections of the eye, particularly of the retina. Nerves and parts of the brain later became part of explanations.