Kodak Enlarging Projection Print Scale, #R26.

The Print Scale is a piece of film divided like a pie, with a number in each of its 10 slices. To use it, you focus the negative, turn off the enlarger, and place a piece of enlarging paper onto the easel with the print scale so that it reads correctly on top of it. Turn on the enlarger for exactly 1 minute with the lens set at f/11. Then process the paper. Pick the section of the pie that looks best. The number in that section will be the exposure time in seconds.