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Why Do My VI Logger Timestamps Seem To Be Off By An Hour?

Primary Software: Other NI Software>>VI Logger
Primary Software Version: 1.1
Primary Software Fixed Version: N/A
Secondary Software:

Problem:
When daylight saving time changes occur, why do my VI Logger historical data timestamps change by an hour (forward or back)?

Solution:
When VI Logger creates a log, the timestamps that it applies are based on the Windows system clock's current time. However, the Windows system clock takes also takes into account the current timezone information. When the Windows system clock is adjusted forward or backward one hour for daylight savings time changes, it effectively moves the computer's current timezone too.

Since VI Logger's timestamps contained in a log are acquired from Windows, the timestamps are then displayed based on how Windows interprets timestamps:

After the spring daylight saving time change, timestamps will be displayed as one hour later.  After the fall daylight savings time change, timestamps will be displayed as one hour earlier

This falls in line with the date / time display philosophy used by Windows: display all times as relative to NOW (which is composed of date / time / timezone information). You can see this same behavior exhibited in the Windows operating system by comparing file creation or modification timestamps before and after the daylight savings time change.

Related Links:
KnowledgeBase 1X12H5RM: How Does Citadel Handle Daylight Savings Time?
KnowledgeBase 3HJHM4XT:  The Current Time Is Incorrect on My LabVIEW Real-Time Controller

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Report Date: 11/01/2003
Last Updated: 01/17/2008
Document ID: 330J3S0U

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