ISO 4217 "ruble". In addition to codes for most active national currencies ISO 4217 provides codes for "supranational" currencies, procedural purposes, and several things which are "similar to" currencies: The use of an initial letter "X" for these purposes is facilitated by the ISO 3166 rule that no official country code beginning with X will ever be assigned. Because of this rule ISO 4217 can use X codes without risk of clashing with a future country code. ISO 3166 country codes beginning with "X" are used for private custom use (reserved), never for official codes. For instance, the ISO 3166-based NATO country
Regional designations of Montana Zones 3 and 4, with limited areas in zone 5 with a small sliver of the state centered in Sanders County in zone 6. These zone boundaries correspond closely to the Köppen classifications. For purposes of the 2009 International Energy Conservation Code, which provides minimum insulation standards for home construction based on climate, the entire state is classified in climate zone 6, reauiring higher levels of insulation than are recommended in more temperate climates. Regional designations of Montana The Regional designations of Montana vary widely within the U.S state of Montana. The state is a large geographical area () that