Hi folks, I'm currently working on implementing a couple of plots to help investigate differences between two similar datasets. I've implemented DifferenceProjectionPlot, RelativeDifferenceProjectionPlot, and AsymmetryProjectionPlot. These are available at my fork of yt https://bitbucket.org/krafczyk/yt under the bookmark 'features/difference_plot'. Essentially, Each of these Plots is a subclass of PWViewerMPL like ProjectionPlot, but create's it's FRB by first creating FRBs for the two data sets then applying an operation to each pixel value to get a new derived value which is a part of the new FRB. For DifferenceProjectionPlot this is simply A-B For RelativeDifferenceProjectionPlot this is (A-B)/A For AsymmetryProjectionPlot this is (A-B)/(A+B) It's already been suggested to me that I can avoid creating three new classes by moving the choice of combination algorithm to a keyword argument, but I'd like to hear more suggestions. Thanks, Matthew Krafczyk