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    HFWG Recommendation R6:

    On the minimum and maximum actual and legal values within columns of FITS tables

    (Approved: 1993 Aug 27)

    If it is necessary to use keywords to store the minimum and maximum values contained within column n of a FITS table, the following keywords should be used:

    • TDMINn
    • TDMAXn

    respectively. These keywords are directly analogous to the DATAMIN and DATAMAX keywords used in association with the primary array and have been adopted elsewhere within the FITS community.

    If it is necessary to use keywords to store the minimum and maximum legal values that may be stored within the elements of column n of a FITS table, the following keywords should be used:

    • TLMINn
    • TLMAXn

    respectively. The following recommentions are also made for clarity:

    • The datatype of the keywords should be the same as that of the table column (n) to which they refer.
    • The keywords refer to all elements of a vector column.
    • These keywords impose no constraints or information regarding the meaning of any null data values within the data.
    • The values of the keywords should be such that they should be compared to the data values stored in the column after those data values have been multiplied by/added to the values stored in the corresponding TSCALn and TZEROn keywords.
    • It should not be forbidden to have values of TDMINn less than TLMINn or TDMAXn greater than TLMAXn, leaving it to individual applications as to what such situations imply.
    • If the keyword for the minimum value be greater than that for the maximum value (i.e. TDMINn is greater than TDMAXn or TLMINn is greater than TLMAXn as appropriate), then this should be taken to mean that the values had not been defined.