A folding frame consisting of six pieces of boxwood 2 x 17.5" (44.5cm) long and 4 x 7.3" (18.5cm) long joined together by two brass hinges and four single leaf brass joints, which when unfolded form a frame. Upper surface of frame graduated 0"-16" by 10ths on top and bottom bars, 0-13" by 10ths on side bars, and 0-180, 180-0 by 30' on side and bottom bars. Reverse surface graduated 0"-16" by 10ths on top and botom bars, 0-360, 360-0 by 30' around the four sides of frame.