Procedure: Drive nail into middle of 28-inch to 30-inch-long 2-by-8, 1/4-inch in from one edge. Then — using the nail as a pivot — swing and slide a framing square so that its corner moves precisely along the 2-by-8's opposite edge. Stop the square frequently as you move it along and, with a pencil, draw a series of overlapping lines along the square's other leg as shown. These overlapping lines will describe a perfect (for this solar hot dog cooker) parabolic curve.
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