In the original FITS format, the members of the data array were required to be of integer data type. Non-integral values, or values outside the range that could be expressed as integers, were stored through the use of scaling. The actual physical values would be derived from the numbers in the FITS file by a linear transformation. The coefficients for this transformation were stored in the header as values of keywords. This method of using integers to represent floating point values has a number of limitations. Only a limited dynamic range of values can be stored with precision using scaled integers. Many astronomical data systems use floating point in their internal data processing; conversion to integers consumes significant amounts of computer time.

The adoption by the IEEE of a standard format for floating point numbers and its widespread implementation by many computer systems provided the solution. On December 22, 1989, the IAU FITS Working Group adopted the Floating Point Agreement, establishing IEEE-754 (IEEE 1985) 32-bit and 64-bit numbers as the standard FITS floating point data types, effective January 1, 1990.