An apparatus includes a baseboard, a grid, a first marker, and a second marker. The grid has a plurality of cells integrally formed with the baseboard. The first marker is integrally formed with the baseboard and intersects the grid at a first angle with respect to a reference line. The second marker is integrally formed with the baseboard and intersects the grid at a second angle with respect to the reference line. The first angle and the second angle are vertically opposite. The grid, the first marker, and the second marker are made of materials having luminescence characteristics that are different than an x-ray characteristic of a material of the baseboard.
