Why is there a bulls-eye in the center of each G7 WhiBal Card?

All WhiBal G7 White Balance Cards come with a focusing grid (bulls-eye) in the center of each card. When taking a reference shot for a custom (in-camera) White Balance, this allows you to stay in AF mode and lock focus onto the card without having to re-compose. If the focus grid were not there, the camera would not be able to lock focus. And if it were in one-shot mode, the shutter release would be locked and the picture could not be taken without resorting to manual focus or re-composition.

Regarding the affect of the bulls-eye on the neutrality of the white balance reading for setting in-camera white balance it has no perceivable effect. That is because the color black is essentially white balance neutral since it reflects no color information. Also, and perhaps even more important, the surface area occupied by the thin black lines is negligible as compared to the neutral gray are of the card. Simply stated the camera does not see the bulls-eye in relation to its white balance computation.