Due to the flexibility of HDS object trees, it is possible to add extra information. Usually such information is recognised only by specific software. In the NDF format, Figaro uses a Figaro extension and a FITS extension. Any extension to an NDF is an object within a `MORE' structure. Since axes are also kind-of NDFs, they can have extensions, too. Figaro is probably the only package to use an extension to axes.
In DST format the information that would be in NDF extensions is not so obvious to locate. The following table translates between objects in an NDF extension and the equivalent in a DST file.
| DST | NDF |
| .FITS | .MORE.FITS |
| .OBS.TIME | .MORE.FIGARO.TIME |
| .OBS.SECZ | .MORE.FIGARO.SECZ |
| .Z.MAGFLAG | .MORE.FIGARO.MAGFLAG |
| .OBS.OBJECT | .TITLE |
| .Z.RANGE | .MORE.FIGARO.RANGE |
| .extra | .MORE.FIGARO.extra |
The FITS extensions in the two formats differ internally. In DST each FITS item is an HDS object. But in NDF format the whole FITS header is an array of strings, and each FITS item is a string in this array.
Needless to say, all but the FITS extension go overboard when you use other foreign data formats. You can inspect the FITS extension with `fitskeys' and add or change items with `fitset'.
FIGARO A general data reduction system