The openings at each end of the caliper are in the ratio of 1:1.61, an approximation to the Golden mean which is actually equal to (1 plus the square root of 5) divided by 2, or 1.618039……  This is made of two pieces of scrap laminate, held together with a little bolt and an acorn nut.  The caliper is about 8 inches long, with the hole at about the 5 inch mark (8/5=1.6; 5/3=1.6).  This little gadget is extremely useful for laying out small pieces on the lathe, for drawing project plans, and for examining images of antique cabinets or buildings (like the Parthenon). Extremely handy. And extremely simple.