How Outlook handles time zone offset and DST rules in calendar items This method is a world standard, and it is how Microsoft implements time on your computer. The formula that is used to calculate computer time is as follows:īe aware that this method represents how people have agreed to think about the concept of time. You can select Change date and time settings to examine the current time zone settings for your computer (Screenshot for this step is listed below).Ĭomputer time is calculated by taking UTC time, adding an offset that is based on the time zone configured for your computer, and then optionally adjusting the offset for daylight saving time (depending on the DST rules).
#Coordinated universal time utc clock windows
If you select this part of the Windows notification area, an enhanced calendar and clock are displayed. HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformationĬomputer time is the actual time that is displayed by Windows, as seen in the following screenshot of the notification area. The Windows current time zone settings are stored in the Windows registry under the following subkey: The Windows current time stores the set of rules that is currently being used to calculate time on your computer.
Of all the rules in the Windows global time zone database, only one set of DST rules can be applied. Windows current time zone settings are the settings Windows is currently using to determine the time for your computer. HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones The database is stored in the Windows registry under the following subkey: Windows stores all time zone and DST rules for the whole planet in the Windows global time zone database. For example, in the summer, the time in the Pacific Time Zone may be calculated as UTC ‒ 7 hours, whereas for the rest year, the time is calculated as UTC ‒ 8 hours. These rules include both a start date and an end date for the DST period and also the number of hours for the time zone offset. UTC, the time in the Pacific Time zone is noon.ĭaylight saving time rules are the rules by which certain regions seasonally change their time zone offset. For example, the Pacific Time zone is 8 hours behind UTC.
Time zone offset is the time for your geographic region in relation to UTC. Think of this as the true time on planet Earth that never changes (except for minor leap seconds here and there to account for changes in the planet's rotation).įor more information about UTC, see Coordinated Universal Time. UTC signifies Coordinated Universal Time. More informationīefore we examine the details of how time zone normalization works in Outlook, it is important to define some important terms.
This article describes how Microsoft Outlook 2010 and later versions achieve this goal by using a combination of items such as Coordinated Universal Time (UTC), time zone offset, daylight saving time (DST) rules, and Windows time zone settings. Although time may seem like a simple human concept that lets everyone across the globe receive a meeting request and then attend the meeting at the same time, the concept is actually very complex.
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