To find the current time in each of the world's different time zone, find the local time and longitude of a current location and that of a new time zone. There are 24 time zones for Earth and each hour measures 15 degrees along its access from east to west.
- Find the difference between the two points
- Add or subtract depending on where the destination is located
For destinations on the same side of the prime meridian, or zero degrees, the two numbers are subtracted, then divided by 15 to find the difference in hours between the two points. For two places on different sides of the prime meridian, the two numbers are added and then divided by 15 to find the difference in hour increments between each of the time zones.
To determine if the hour difference is earlier or later than the first location specified as the constant, use the prime meridian and east and west as a guide. If the location that the time is needed for is to the east of the constant, then add the difference to find out the new time. If the location is to the west, then subtract the final number to find the time.