This is the first of a two-part description of a new software tool CRUST (Climatic Research Unit Standardisation of Tree-ring data). This program has been designed primarily to allow the convenient, routine application of "Signal-Free Regional Chronology Standardisation" (SF RCS) to different types of tree-ring data. The program also enables the use of other popular standardisation methods. A series of experiments is described in which the ability of simple RCS and SF RCS to recover known tree-growth forcing signals is tested. In the comparatively rare situation where many sub-fossil data are distributed over a wide time range and there is no slope in the overall common-growth forcing signal, simple RCS is satisfactory. Simple RCS produces distortion in all other examples explored here. SF RCS is superior to simple RCS and in all cases examined. SF RCS works well except when the span of starting dates of sample trees is too narrow, a situation for which a test is available. Based on the results of the tests explored here, we conclude that Signal-Free RCS should be used as the standard method of RCS processing.