For platemaking, the Stouffer Gauge is the most accurate way to figure out the exposure time for your letterpress photopolymer plates. The gauge is a reusable piece of film that you treat as a normal positive or negative while you process a small test plate. Place the Stouffer gauge on a small square of photopolymer and expose per instructions. Use the Correction Table to increase or decrease your exposure. To determine your exposure reading, read the lowest number of solid relief visible next to the clear exposed section of the stouffer. Gauge measures ½” x 5”.