Accuracy Grid
3x3 grid of fixation targets at four different distances from the wearer.
On application start the grid is attached to the main camera to always present at front of the wearer. If triggered to display, e.g. by the control interface, the culling mask of the main camera is modified to hide all layers except for the accuracy grid layer. On hiding the grid the previous culling mask is restored.
Game objects of the grids at the four distances and the Unity layer to which the grid is assigned to.