Rating Period 2 : The period of time, usually a 24 hour period extending from midnight to midnight, during which a fire danger rating value is considered valid
Ralph W. Burklin & Robert G. Purington, Fire Terms: A Guide to Their Meaning and Use, National Protection Association, Boston, MA 1980 USA. (Guide: Meaning and Use, Nat Prot Association Fr Srvc - Amer) {457}