The Delta 1 CPM 22010 18% Gray Card is an accessory used to help determine the correct exposure for film and video. The card has been colored a special shade of gray, which is designed to provide an ideal standard for measuring mid-tones as the basis for exposure and color settings, as it is chromatically uniform and spectrally neutral.

The 18% Gray Card has two primary uses: for providing a standard subject for light-metering, and for white-balancing.

When used for light-metering purposes:
With a reflective light-meter, the reading given will be the same as that given from an incident light-meter. This is assuming that the card is positioned correctly, with respect to the light-source and the meter. The reading given by the light-meter will represent the correct exposure setting for the mid-tones only — the exposure of the shadows and highlights will depend on their difference in illuminance as compared to the mid-tone exposure given by the Gray Card.
With a camera or camcorder’s built-in meter, the device will deliver similar readings, when set to adjust exposure automatically. For manual exposure, the broadcast standard is approximately 50% IRE, for camcorders that display brightness information as a percentage. Consult the manufacturer’s operational manual for instruction on how to interpret the camcorder’s exposure readings.

When used for white-balancing purposes:
Once the desired exposure has been set, it is also possible to use the Gray Card for white-balancing. This may seem counter-intuitive, as calibrating the color-balance electronically is called “white-balancing” — however, white-balancing to the Gray Card will actually render a more accurate representation of color than using an improvised white surface. The shade of gray of the Gray Card is a special formulation of hue and saturation that is neutral in both chroma (color) and luma (brightness). The human eye is easily fooled into perceiving an off-white color as true white, and calibrating the camcorder to these false-white surfaces will cause the entire color spectrum to “shift” accordingly. It will render the off-white as true white, but all the other colors will be skewed relative to the referenced-white surface’s chrominance.
Using the Gray Card consistently for white-balancing throughout a shoot or production will ensure that all colors are accurately represented, as the camcorder will be referencing a spectrally-neutral standard. This can greatly expedite the color-correction process in post, as all of the colors displayed will be consistently “placed” relative to a constant and neutral chrominance standard.

A technique often used for still-photography, but useful to videography as well, is to take a shot of the Gray Card for each take or scene, to provide the editor with a reference subject for adjusting Hue, Saturation, Brightness, and Contrast in post-production.