The Java-sourced time zone database has a “historical perspective,” where a history of changes for applicable time zones are stored. Thus, multiple definitions for a time zone may exist, including past definitions as well as its current definition.
This allows display of a station’s timestamped data (histories and alarms) collected in time zones under “prior rules” (typically
DST-related) to display with the original (and correct) collected time.
NOTE: On all
Niagara 4 JACE controller platforms, the Java-sourced time zone database is historically accurate only back to year 2010. Any pre-2010 historical
data is displayed using 2010 rules. This was done to improve Java heap usage on these platforms.
However, note the Java-sourced time zone database on Windows
Niagara 4 platforms extends further back, for example, to year 1995.
In
Niagara 4 Workbench, use the Time Zone Database Tool () to navigate the Java time zone database, where you can explore DST rules for any timezone. If a local station is running
on the same host (
Supervisor), this is time zone database that is utilized. For more information about the Time Zone Database Tool, see the section by
the same name in the User Guide.