Comparing the results of multiple related simulation databases is one of VisIt's main uses. You can put plots from multiple databases in the same window or you can put plots from each database in adjacent visualization windows, allowing you to compare plots visually. In addition to these visual comparison modes, VisIt supports more direct comparison of databases using database comparisons. Database comparison allows you to plot direct differences between two databases or between different time states in the same database (i.e. time derivatives). VisIt's expression language is used extensively to facilitate the database comparison.