An apparatus includes a first end and a second end opposed to the first end. A body connects the first end to the second end. The second end includes a mark in a center of the second end, a first plurality of marks positioned on a first axis, a second plurality of marks positioned on the first axis on an opposite side of the center mark as the first plurality of marks, a third plurality of marks positioned on a second axis, a fourth plurality of marks positioned on the second axis on an opposite side of the center mark as the third plurality of marks, a fifth plurality of marks positioned on a third axis, and a sixth plurality of marks positioned on the third axis on an opposite side of the center mark as the fifth plurality of marks.