FALTER is a program that supports the process of determining the effect of a program defect on the local program state. FALTER also provides the capability of recording the effect by annotation of the program control flow graph. FALTER is one of a series of four tools that work in an integrated fashion to analyze Pascal programs to determine the failure regions associated with identified faults in the programs. The annotated control flow graph produced by FALTER will used as input by the program SPACER, and shall be customized for such usage. The users may access REACHER, FALTER, and SPACER through a screen oriented user interface called VIEWER. Beyond the failure region analysis FALTER may be useful in research that examines the distribution of faults in program source code, and in efforts that examine the erroneous transformations induced by faults.