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11/01/2009

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Web applications can get the users local timezone through JavaScript.

You can get the offset using javascript, then send that to the server

Great post. I had a lot of reporting errors awhile back due to dealing with multiple servers with multiple time zones. Crazy!

General location can be inferred from IP address. A number of services are available, just google "IP Location Finder". They're pretty rough, but they'll get you in the ballpark.

> we have three main use cases here (there are some others)

What are they?

> If I missed an interesting use case, please let me know

* Off planet Earth times, ie. the Mars Rover time, and other planet local times

* Different cultures' ways of expressing time and dates (ie. Hebrew, Chinese, Mayan, many more)

* Warps in time due to travel at very high speeds (ie. very precise times on super sonic aircraft)

Good post. One point, though. UTC is not the same thing as GMT.

You said:
Interesting note, UTC only matches the time in Greenwich during standard time. When it is DST there, Greenwich and UTC are not identical.

GMT is not always the time at Greenwich England. GMT is always within a second of UTC. GMT (now called UT1) is preferred because it always has 24*60*60 seconds in a day.

.NET 3.5 includes DateTimeOffset: http://msdn.microsoft.com/en-us/library/system.datetimeoffset.aspx
which is the same datatype SQL Server 2008 has support for.

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David Thielen

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