By employing a rectangular mesh the support value of the grid has been increased, offering a value intermediate between the most commonly used grid (200 Lines/") and (300 Lines/"/). Each grid rectangle is asymmetrical having different outlines in all four corners. This allows for the orientation of the grid to be determined at microscopic levels. The index feature enables the position of each grid to be identified with reference to the letters A-O along the horizontal axis and the numbers 1-15 along the vertical axis. The logo in the rim allows for precise orientation and aids in the identification of each side. Grids are available in Copper, Copper/Palladium, Nickel, and Gold.