In the development phase, the new GIO library is still able to write down the old data format. Besides the inherent limits of the GDFV1 format (4 dimensions only, GBytes only), this means a number of additional restrictions.
For UV tables, in particular, there must be no non-standard column (i.e. the only authorized non-zero h%gil%column_pointer are those in the range 1-7), no polarization information or irregularly spaced channels.
This facility is provided for debugging only, but not intended to be made available to general users. It is controlled by the logical name GILDAS_HEADERS (which is used by all tasks) and, in SIC driven programs, also by command SIC HEADERS, so that one can temporarily write in the old format if needed. This capability will become obsolete once the transition phase to GDFV2 is complete.