The graph algorithms create random adjacency graphs when breaking ties for the location of department nodes in the adjacency graphs. When graph algorithms are executed again with a different seed, a different graph might be generated. The layout improvement algorithms based on simulated annealing select random pairs of departments to be tested for possible exchange. Different replications of the same algorithm can thus provide different adjacency graphs or block layouts. The higher the number of replications, the more likely a high quality block layout will be constructed. But this comes at an increase in computation time. You can set the maximum number of replications the graph algorithm executes with the Max. Replications command of the Edit menu.