Keywords not defined by the PDFs

It should be noted that there are a number of keywords which are not defined by the PDFs. These are:

• Keywords which refer solely to the way in which the FITS tape itself is written ( e.g. SIMPLE, BITPIX, BLOCKED, BSCALE, BZERO, TAPENAME, END). These keywords must be added by the software that creates the FITS files.

• The mandatory keywords NAXIS and NAXISn should also be determined by the FITS-writing software at the point of writing to tape, in order to ensure consistency with the data-array.

• It is possible for the observer to specify an arbitrary number of comments during an exposure, which will be written as COMMENT records to the FITS header.