The ODEON model for room acoustics is implemented for general use on a PC. Technical features of the program relevant to the acoustical design process include interactive visualizations of reflection paths and sequences, mapping of overall energy distributions and of coverage provided by individual reflectors, and minimized recalculation times. In this paper the modelling process is discussed. Comparisons are then made between predicted room acoustical indices and values measured in full-size and model halls, and reasons for discrepancies are discussed. These discrepancies indicate areas in which the computational model has to be improved, and highlight some shortcomings of current room acoustical survey methods. The effects of various calculation parameters (e.g number of rays, early reflection order) are also briefly considered.