One side of the card has a neutral 18-percent reflection which can be used indoors to aid in measuring the average reflection for a typical subject. You can also use this side of the card outdoors by increasing the exposure 1/2 stop above the calculated exposure. The other side of the card has 90-percent reflection for use at low- light levels. The use of this card and appropriate adjustments for aperture and exposure time is covered in Kodak Gray Cards, Kodak Publication No. R-27.