The development of precision grammars is an inherently resource intensive process. In this thesis we investigate approaches for providing grammar engineers with greater feedback on the impact of changes made to grammars. We describe two different visualisations which are created by comparing parser output from two different states of the grammar. The first involves the ranking of features found in parser output according to their magnitude of change so as to provide a low-level picture of the affected parts of the grammar. The second involves performing clustering over sentences whose parsability has changed in an attempt to find related groups of changes and accompanying sentences which exemplify each locus of change. These approaches provide complimentary avenues of feedback which can hopefully improve the efficiency of the grammar engineering development process.