Hair growth measurement. Female researcher using a video microscope to measure hair growth on a man's scalp. Magnified on the monitor (lower left) is an image of the man's hair seen a few hours (yellow & green) and a few days (red) after it was shaved. Hair on the scalp typically grows 1 cm each month. Photographed at the Laboratoire de L'Oreal in Clichy, near Paris, France.