An excellent picture is produced with a precise exposure. If the light in scene is excessively bright or dark, exposure deviation might be produced.
Gray card can balance all mixed lights to be 18% neutral gray. With a photometer, you'll get precise exposure value by recording the light that is reflected from the grey card.
It is 100% waterproof which is sound for underwater photography to eliminate the underwater blues.
Weight: 14.5 ounces/411 grams
19.2 x 9.84 inches/49 x 25centimeters
2 x Gray Card