Before the 19th century, people kept their clocks accurate by observing the sun and stars, so dusk and dawn occurred at different times, based on geographic location. After the 19th century, it became possible to travel between time zones with much greater speed, necessitating the need for a time-keeping system that worked worldwide. While the The U.S. has six time zones altogether, converting between two of these, Central versus Pacific or West-Coast Time, is a matter of using mathematics.
Understanding Time zones
In the U.S., the Pacific Time Zone, which is also called West-Coast Time, is separated from the Central Time Zone by one time zone, called the Mountain Time Zone. As you travel across the country going east, you add an hour for each time zone. For example, If it is 12 p.m. in the Pacific Time Zone, it's one hour later that that, which is 1 p.m., in the Mountain Time, and two hours later, 2 p.m., in the Central Time Zone.
If you know the time on the west coast, which is in the Pacific Time Zone, and you want to know what time it is in the Central Time Zone, add two hours to the West Coast Time. Similarly, if you know the time in the Central Time Zone but want to know what time it is on the west coast, subtract two hours from the Central Time Zone time.
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