In presenting the basic principles of these two disciplines, I've oversimplified somewhat for the sake of brevity. You exchange the goods for the pennies and place the item on the two penny table. Depending on the equipment, the lens may be held in place by special adhesive pads, with a special alloy that "glues" the lens to the block or with plastic. As it operates, the slowly turning lens is brought into the fast turning cutting surface, which is either a grinding wheel or steel blades, until a guide contacts the pattern, which is rotating to match the lens. 2.50 cylinder, for example, to match -2.00/-2.50 generated curves), and the lens and block are rubbed together. For example, the vast majority of labs now use computers to determine curve parameters and lens choice, and equipment is available that will combine several steps or even do the entire operation automatically. If the lens gets too hot during the operation it may warp or tear, so it is cooled by water, which also washes away the cut material (called scarf). Newer edgers do not use patterns; instead, the shape is determined by a probe that measures the frame and stores the information in a computer, which in turn controls the edging operation.