The Delta 1 Projection Print Calculator Scale makes your job easy of developing photos in darkrooms. This scale can be used to determine the required number of seconds to get the correct exposure for the photographs. It has a circle with eight partitions that have seconds on their top to indicate the exposure time. To test the exposure, place the scale on the sensitized paper and then expose the paper for 60 seconds with the negative enlarger. You can choose the number of seconds to expose the picture by referencing the ideal looking circle sector. The projection print calculator scale saves your time, paper, and money when developing photographs.