The Macbeth ColorChecker is the traditional standard for visual and measuring reference.
This target is available in the "standard" size only.
Also, the gray patches on the ColorChecker are considered some of the most neutral available - more neutral than most Kodak targets. For gray balance on digital cameras, this target is a must-have.
The White Balance card is a full-size version of the white reference square on the standard ColorChecker. This white is scientifically engineered to provide a precise, uniform surface that is spectrally neutral in all types of light conditions.
The Custom Grayscale card is an 8/5 x 11", spectrally neutral three-step grayscale card engineered to provide quick studio lighting balancing. This card is used to quickly determine the maximum lighting ratio for the fill and main lights in the studio.
Shown above: Grayscale Card