Blades are about 3/16 inch (4. 7 mm) thick. When viewed from the side, the blade of a figure skate is not flat, but curved slightly, forming an arc of a circle with a radius of 180–220 cm. This curvature is referred to as the rocker of the blade. The “sweet spot” is the part of the blade on which all spins are rotated; this is usually located near the stanchion of the blade, below the ball of the foot. The blade is also “hollow ground”; a groove on the bottom of the blade creates two distinct edges, inside and outside. The inside edge of the blade is on the side closest to the skater; the outside edge of the blade is on the side farthest from the skater. In figure skating, it is always desirable to skate on only one edge of the blade. Skating on both at the same time (which is referred to as a flat) may result in lower skating skills scores. The apparently effortless power and glide across the ice exhibited by elite figure skaters fundamentally derives from efficient use of the edges to generate speed.