Time_Terminology

   Absolute time is a point on a time scale; absolute time
   measurements are derived from system clocks or external time-
   providers. For DECdts, absolute times reference the UTC standard
   and include the inaccuracy and other information. When you
   display an absolute time, DECdts converts the time to ASCII text,
   as shown in the following display:

   1996-11-21-13:30:25.785-04:00I000.082

   Relative time is a discrete time interval that is usually added
   to or subtracted from an absolute time. A time differential
   factor (TDF) associated with an absolute time is one example
   of a relative time. Note that a relative time does not use the
   calendar date fields, because these fields concern absolute time.

   Coordinated Universal Time (UTC) is the international time
   standard that DECdts uses. The zero hour of UTC is based on
   the zero hour of Greenwich Mean Time (GMT). The documentation
   consistently refers to the time zone of the Greenwich Meridian
   as GMT. However, this time zone is also sometimes referred to as
   UTC.

   The time differential factor (TDF) is the difference between UTC
   and the time in a particular time zone.

   OpenVMS systems do not have a default time zone rule. You
   select a time zone by defining sys$timezone_rule during the
   sys$manager:net$configure.com procedure, or by explicitly
   defining sys$timezone_rule.

   The OpenVMS time structure is based on Smithsonian time,
   which has a base date of November 17, 1858. The binary OpenVMS
   structure is a signed, 64-bit integer that has a positive value
   for absolute times. You can use the DECdts API to translate an
   OpenVMS structure representing an absolute time to or from the
   DECdts UTC-based binary timestamp.

   For detailed information about DECdts time representations, refer
   to the VSI OpenVMS Utility Routines Manual.

   Unless otherwise specified, the default input and output
   parameters for the DECDts API routine commands are as follows:

   o  If utc is not specified as an input parameter, the current
      time is used.

   o  If inacc is not specified as an input parameter, infinity is
      used.

   o  If no output parameter is specified, no result (or an error)
      is returned.