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By Tom Groom, VP, Consulting Group, D4 LLC
In a previous blog, we explained why D4 recommends as a best practice to process ESI with the UTC standard (Coordinated Universal Time). Many questions arose from that blog with the most popular being “isn’t processing ESI in the GMT time zone the same thing?” This blog will answer that question and round out the topic of time zones altogether.
A time zone is a region on earth that has a uniform standard time for legal, commercial, and social purposes. It is convenient for areas in close commercial or other communication to keep the same time, so time zones tend to follow the boundaries of countries and their subdivisions.
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There are 24 time zones in the world. If an event happens at 11:00 a.m. in Houston, Texas, it would be reported at 12 p.m. in Orlando, Florida; 4:00 p.m. in Morocco; 9:00 p.m. in Kolkata, India; and 6:00 a.m. in Honolulu, Hawaii. The event happened at 4:00 p.m. UTC.
Most of the time zones on land are whole number offsets of hours (UTC−12 to UTC+14) from Coordinated Universal Time (UTC). Some higher latitude countries such as the United States use daylight saving time for part of the year, typically by changing clocks by an hour. For example, the Eastern Time zone is UTC-5 for Eastern Standard Time (EST) in the fall/winter and UTC-4 for Eastern Daylight Time (EDT) in the spring/summer.
GMT is a local time zone based on the Prime Meridian at Greenwich, United Kingdom. The Prime Meridian is the zero degrees longitude line that divides east from west around the Earth. GMT was established in 1886 (way before computers and international time standards were even concepts).
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UTC is also based on the Prime Meridian, which may be why some equate UTC with GMT. Most all timekeeping devices use this 24-hour time standard based on highly precise atomic clocks. The hours, minutes, and seconds that UTC expresses are kept close to the mean solar time at the Earth’s prime meridian. Just as the prime meridian is the standard for east/west longitude, UTC is the standard for coordinating time worldwide. It is important to keep in mind: UTC is a universal time standard and not a local time zone.
The prime meridian also helps establish the International Date Line. The Earth’s longitude measures 360 degrees, so the halfway point from the prime meridian is the 180 degree longitude line. The meridian at 180 degrees longitude is commonly known as the International Date Line. As you pass the International Date Line, you either add a day (going west), or subtract a day (going east.)
So, what time is it in your local time zone? What day of the week is it? Your answer depends on where you are on the earth and what time of year it is (assuming you’re in a location that observes daylight savings time). UTC – not a zone, but rather a formalized standard for coordinating time on earth. It just so happens UTC and GMT share the same baseline, the Prime Meridian. UTC-0 expresses the GMT time zone.
Bottom line, for ESI and discovery, it makes sense to process data in the standard in which it lives, namely UTC. Anything else would be “localizing” it to a specific region on the earth and time of year, which often leads to confusion, added costs and unnecessary disputes. There are two exceptions to that recommendation as stated in the previous blog, but they should only be used as “Plan B”. Our recommendation is to keep it simple – keep ESI in UTC.
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