DGK Color Tools R-27, 18% Gray White Balance and Exposure Control Card Set, (Set of Three Cards, Two 8x10" and One 4x5") Set of 3 extra thick cards - each 18% gray front, black back Used for white balance, exposure, adjusting lighting ratio and checking light distribution in video, cine, film, and digital Genuine DGK Color Tools - Designed in Boston and made in USA Spectrophotometer verified 18% reflectance. Package contains two 8 x 10 x 1/16" extra thick cards and extra thick pocketable 4 x 5 card