What every programmer should know about time
> Timezones are a presentation-layer problem!<p>I want to correct this common misconception that UTC is enough. Calendar time with all human traditions involved is more complex than a simple timestamp.<p>The advice above is incorrect for calendar and scheduling apps, or anything that has a concept of a repeating event.<p>An example: we have a weekly meeting occurring 9AM Monday in San Francisco. You are in London and want to attent the meeting over Skype. When is it in London time?<p>It depends.<p>On  7 Mar 2011 it's at 5pm<p>On 14 Mar 2011 it's at 6pm<p>On 29 Mar 2011 it's at 5pm<p>To make these calculations, you need to know timezone & daylight saving time (DST) rules of both your current location and the home location of the event.<p>A "DST zone" of a home location of a repeating event has to be saved together with a time and thus it's not just presentation-layer issue.