If you’ve ever been startled out of a sound sleep by a transcontinental phone call, you already know how time zone differences can impact your life. Four zones went into effect in the United States, in November 1883, when railroads attempted to standardize local time to make train travel and shipping more efficient. The Eastern, Central, Mountain and Pacific zones cover the continental U.S. and Canada. Converting times from one zone to another only requires solving a simple math equation.
Finding the Time
As you move from the east coast of the United States to the west across time zones, you subtract one hour for each zone. The mountain zone is two zones away from the eastern zone, so you subtract two hours. For example, if it is 10 p.m. in the east, it is 8 p.m. in the mountain zone.
Exceptions to Every Rule
For approximately half of the year, the conversion is just that simple. However, between the second Sunday in March and the second Sunday in November, Daylight Saving Time makes things slightly more complicated. Except for the Navajo Indian Nation, the state of Arizona does not observe Daylight Saving Time. During that part of the year, to convert from Eastern Time to Mountain Time, subtract three hours instead of two.