0                  Indicates success.
    -1                 Indicates an error; errno is set to one of the
                       following values:

                       o  EINVAL - The clktyp argument does not
                          specify a known systemwide clock.

                          Or, the value of SYS$TIMEZONE_DIFFERENTIAL
                          logical is wrong.

                       o  EIO - An error occurred when the systemwide
                          clock specified by the clktyp argument was
                          accessed.