Phi (or the golden ratio as it is also known) is a value of 1:1.6180339. Named to honour Phidias, the lead sculptor of the Parthenon in Greece, this unique number plays a prominent role in architectural and furniture composition and design, where it is used to proportion objects for aesthetic appeal. In woodworking as an example, tabletops are usually about 1.6 times longer than wide. Dining chairs often have backrests that are about 1.6 times taller than the seat height. The most appealing drawer proportions, and their placement, are also typically related by Phi. In turning, use of Phi helps guide height vs. diameter proportions. These rules simplify Phi calculation and proportioning during design (and help identify the golden ratio in existing objects). They have a dual scale with normal graduations on the top edge and Phi-scale graduations on the bottom edge. Both faces are graduated; one face converts a known long measurement to an unknown short measurement, and the other face does the opposite. To scale a measurement, you simply find the identical measurement from the top scale on the lower scale. The hardened stainless-steel rules have a matt finish, ground edges and black-filled etched markings. Excellent layout aids, they are available in 12" lengths.