The QPcard 101 Calibration Card is a small, lightweight, and inexpensive way to calibrate your white balance. Three QPcards come in a protective envelope that fits easily into a camera case or pocket. There is a millimeter reference scale on edge the card.
The cards have adhesive on the back, so they can be attached to virtually any surface.
The gray surface is completely neutral and reflects 18% light, with a white and black patch that can be used for contrast adjustment as well as a dimensional reference.
A guaranteed neutral gray surface in the image simplifies color balancing.
With correctly set and calibrated computers, software, and monitors, start with a white-balance reference image.
Smaller than carrying around a larger gray card, it is small enough to place it next to the subject.