Hiding Heidi Low Contrast Face Test are available in 2 different versions:
Double Sided (Item # GF3500): Four cards printed on both sides in the following contrast levels: black, 25%, 10%, 5%, 2.5%, and 1.25%.
Single Sided (Item # GL3510): Seven cards printed on one side in the following contrast levels: black, 25%, 10%, 5%, 2.5%, and 1.25%.
Cards are 9" x 9" (23 cm x 23 cm). Includes instructions.