READ Optimisation

        Reading can be lengthy, especially for ALMA data.   IMAGER  attempts  to
    minimize  read operations by checking if anything has changed since the last
    command.  This capability is enable if the SIC variable MAPPING_OPTIMIZE  is
    non zero, disabled otherwise.

      Currently,  the  READ  command always display a message about what reading
    may have been skipped, and whether this possible optimization has been over-
    ridden by user choice.