This subroutine returns the number of header items or the number of occurrences of a specific item. The numbers returned can be used as limits when indexing using HDR_NAME or when deleting/reading items with more than one occurrence (such as FITS ’HISTORY’ or ’COMMENTS’) or to test the existence of an item.

CALL HDR_NUMB( PARAM, XNAME, ITEM, N, STATUS )

PARAM = CHARACTER $\ast$ ( $\ast$ ) (Given)

XNAME = CHARACTER $\ast$ ( $\ast$ ) (Given)

ITEM = CHARACTER $\ast$ ( $\ast$ ) (Given)

N = INTEGER (Returned)

STATUS = INTEGER (Given and Returned)

• This subroutine will directly access an image if an association has not already been made. Note that it will be opened for read-only access and you will not be able to write or delete any header items. If you need to be able to do this then access the image first, either with one of the ??x]]IMG_MOD[n][x] subroutines (if you intend to process the image data), or the HDR_MOD subroutine.

• This subroutine may be used to query the number of items or occurrences of an item in the same source of more than one image dataset at a time by using multiple parameter names. Multiple parameter names are provided as a comma separated list (i.e. ’IN1,IN2,IN3’). The source must exist in all images and the argument N will be returned as the maximum number of header items or occurrences located (from each source).

• If the number of header items is zero then this will be returned, no error will be reported.

• The number of occurrences of an item will usually be 1, except for the special FITS items ’COMMENT’, ’HISTORY’ and ’’. This ability is therefore most useful for testing the existence of items (0 is returned if an item isn’t found) or for manipulation of the occurrences of the special FITS items.