To use FFREAD, the user first identifies a variable or array he wishes to set up by a key. These variables and arrays should be in COMMON; the use of local variables can lead to problems with optimizing compilers. After calling an initialization subroutine, he then defines each key he wants to use to the system, giving its location, type (real, integer, or logical), and length (for arrays). When he has defined all keys, he can at any time during his program call the main subroutine of FFREAD, which will read in the data cards and modify the variables in memory accordingly.