With more than 40,000 customers, the Genuine WhiBal has become the standard in the industry for precision WB Reference "Gray Cards". Each and every card is measured with a precision spectrophotometer to assure you that *your* card meets our industry leading specification of /-0.5 within the a* and b* channels.
Do not be fooled by RGB measurements (they have no meaning in this context). Very simply, WhiBal combines all the best features of all available White Balance cards, and meets or exceeds their technical performance in a unique package that can be used conveniently in all your shooting situations.
In addition, WhiBal provides convenient neutral White and Black reference areas for setting dynamic range in your digital capture using the Black and White Eyedroppers available in RAW conversion software, PhotoshopTM, and most other editing software.
Check out the educational videos on-line. (Search for WhiBal). They tell the entire story.

Feature Summary:
It fits in your shirt pocket.(2.1x3.35 inches)...so you will actually use it rather than have it in your bag!
It is basically indestructible, waterproof, etc
All 4 reference "colors" are essentially equal to or better than all tested "reference cards" for neutrality and spectral flatness.
All cards are designed for low reflectivity, except the BlackPoint sticker which intentionally is highly reflective so that maximum Blackpoint level may be achieved.
Can be used to set white balance reference, Black point and White point.
Fits shirt pocket or can hang on studio hook.
WhiBal is a product of PictureFlow LLC, is patent-pending and proudly made in the USA.