The Compress method will make a domain use less space - in particular if there are many deterministic dependencies in the network (many zero-values in node tables). If results are not required to be absolutely precise, one can use the Approximate method to make the least probable configurations impossible by setting their probability to zero. This will make Compress even more effective. Thus, the purpose of calling Approximate should be to call Compress right after. The Approximate method takes one argument - a constant used as a threshold to eliminate low-probability configurations. For performance reasons it is not possible to remove exactly a least probable probability mass. The ApproximationConstant property can afterwards tell the effect of using Approximate with a particular threshold.