HP Marketing Corp., Pine Brook, N.J., has new Zebra cards from Novoflex for photographers to check white balance in the field. The Novoflex cards have been measured to be within 0.03 density between R, G and B and have no UV peaks, the company claims. The flexible cards, made from a special polymer, have an antireflection coating on both the white side and the grey side. The grey side serves as a reference area for exposure metering while the white side enables correct white balance. For prolonged service the Zebra cards are washable. The 9-by-6 inch cards are $27.99 and the 12-by-8.3-inch cards are $34.99.