from the Boone and Crocket web site:
All measurements must be made with a 1/4-inch wide flexible steel tape to the nearest one-eighth of an inch. (Note: A flexible steel cable can be used to measure points and main beams only.) Enter fractional figures in eighths, without reduction. For example, if a point measures 7 and 2/8 inches, you would enter 7 2/8 in the space provided.