RESOLUTION A4
 
 ON THE MODIFICATION OF DATE VALUES ON FITS SOFTWARE

   The XXIIIrd International Astronomical Union General Assembly,
 Recognizing
       that the two-digit year numbers in the date values of keywords such as
       DATE-OBS='31/12/99' in FITS files will become ambiguous on the day 2000-01-01,
   and noting
        that the IAU FITS Working Group has adopted new rules for DATExxxx
     value strings which specify that the previous convention applies only to 
     dates in the range 1900-1999 and that the new convention DATE-OBS='1999-12-31'
     is to be used in data interchange and in data archives beginning 1998-01-01,
   Urges all IAU members
             to ensure that their FITS writing and reading software is modified before
          1998-01-01 to support both the new convention and the old convention, in
          accordance with the rules specified by the IAU FITS Working Group.

Reference: Transactions of the International Astronomical Union (1997), Vol. XXIIIB, p. 35.