SYSTEM_CLOCK ([count] [,count-rate] [,count-max])

  Class:  Subroutine

  Returns integer data from a real-time clock.

  All arguments are scalar of type default integer.  The "clock" is
  set to a value based on the current value of the processor clock.
  The value is increased by one for each clock count until the value
  "countmax" is reached, and is reset to zero at the next count.
  ("count" lies in the range 0 to "countmax".) The "count-rate" is set
  to the number of processor clock counts per second modified by the
  kind of "count-rate." See the HP Fortran for OpenVMS Language
  Reference Manual.

  SYSTEM_CLOCK returns the number of seconds from 00:00 Coordinated
  Universal Time (CUT) 1 JAN 1970.  The number is returned with no
  bias.  To get the elapsed time, you must call SYSTEM_CLOCK twice,
  and subtract the starting time value from the ending time value.

  Examples:

  Consider the following:

    INTEGER(2) :: IC2, CRATE2, CMAX2
    INTEGER(4) :: IC4, CRATE4, CMAX4
    CALL SYSTEM_CLOCK(COUNT=IC2, COUNT_RATE=CRATE2, COUNT_MAX=CMAX2)
    CALL SYSTEM_CLOCK(COUNT=IC4, COUNT_RATE=CRATE4, COUNT_MAX=CMAX4)
    PRINT *, IC2, CRATE2, CMAX2
    PRINT *, IC4, CRATE4, CMAX4
    END

  This program was run on Thursday Dec 11, 1997 at 14:23:55 EST and
  produced the following output:
    13880   1000  32767
    1129498807       10000  2147483647