Grooves have been made in each of the four sides of the frame. In every groove are two moveable knobs, to which the drawing tools can be attached. The graduation, which is at all sides of the frame, indicates 5 centimeter distances (little slots next to the drawing surface), indicates every centimeter at the inner side of the groove, and every 0,5 centimeter at the outer side of the groove.
For measure designation in centimeters, 9 millimeter wide semi-circular hollows have been made on a short distance from the edge. They create points between them, each with a distance of 1 centimeter to the next. With those points, it becomes easy to read the exact distance per centimeter. Because the hollows are semi-circular, the distance per 5 milimeters can be read in the deepest point of the hollow. The measure designation can be found at all edges of the drawing surface and on the drawing tools. An exeption is the round edge of the protractor. Here the points between the hollows don’t indicate 1 centimeter, but indicate the angle in steps of 10 degrees instead.
Knobs and holes
Black ribbed knobs can be moved through the grooves by (un)screwing them. The knobs are 2 centimeters wide and 8 milimeters high. They can be removed by totally unscrewing them. To place a knob back in the groove, place it on a random place in the groove, and slide it all the way to the outer corner, dragging the nut along. Here the knob can be screwed again.
The drawing tools have holes and wide grooves, to fit around the knobs. By fixing the knob and putting the tool over it, the tools can be tightened. With partially unscrewed knobs, the tools can smoothly be moved across the drawing surface.