Two glass panes with concentric mirrored rings are positioned one in front of the other, with the centre point of the rings eye-width apart and situated approximately at eye level. Behind the panes is a polished aluminum mirror set at an angle to the glass. This reflects the back of the rings, which are black. Looking at their reflections in the mirror, viewers are challenged to adjust their stereoscopic sensory powers, and a moiré effect is clearly perceptible.