Timezone Converter

How does this timezone converter function?

The form above has two places, one for the data input and one for the results. The first two fields are the current date and time and you can change according to your needs. Below them there are two lines in which you need to choose the starting point for the international time conversion and the location for which you want to find the corresponding time. In each of the two lines you first need to choose the region in order to narrow your choice. In the “From” section you can choose whether you prefer a state or a capital and then narrow your search to the specific location in the second dropdown. In the  “To” section for the region you can choose from Africa, Asia, Australia, Caribbean, Central America, Europe, North America and South America and for each region you need to decide if you prefer a country or a city. Once you have selected the region the second selection for location will display the countries or the cities in the region you chose in alphabetical order for you to find the desired place easier. As you press calculate the timezone converter will find your locations in a complex database of the world zones, check whether it needs to take into consideration the existence of a daylight savings time and will then calculate the time zone difference between your two locations and return you with the exact time in the second place you chose. The conversion equation used by all time zone conversions: "time in zone B" = "time in zone A" − "UTC offset for zone A" + "UTC offset for zone B".

The concept of Coordinated Universal Time (UTC)

Greenwich Mean Time (GMT) was the first time standard adopted in 1847 and followed time using telescopes and was calibrated to the mean solar time at the Royal Observatory in Greenwich, UK. This time keeping method is less exact than the now used UTC because the rotational period of Earth is not perfectly constant and the duration of a second would vary if calibrated to a telescope-based standard like GMT. 

Since January 1972, UTC was set to follow the International Atomic Time (TAI) with an exact offset of an integer number of seconds. Within this implementation most nations began to use the UTC standard when defining their time zones instead of the former GMT definition. A UTC time offset is the amount of time subtracted from or added to UTC to get the current local time for a specific location. Offsets from UTC are written in the ±[hh]:[mm] format.

Time Zones definition

A time zone is a region on Earth that keeps the same standard time. The time zone map shows that Earth is split up into time zones that are mostly one hour apart. Most time zones are one hour apart and compute local time as an offset from UTC or GMT. The reference point for UTC is the Greenwich Meridian (the Prime Meridian), which has a longitude of 0°.Local time is UTC plus the current time zone offset for the locations situated east to the meridian and UTC minus the current time zone offset for the locations situated westward. Many locations change the offsets during summer months to define the usage of Daylight Savings Time (DST).