PhotoCompute introduces you to the interactions between your camera equipment and the underlying mathematics. It also provides better algorithms for computing DOF, distance to subject, etc., for macro distances than standard programs.
You need to install your camera body, lenses, extension tubes, and flash units into the program. This allows for accurate computations, and makes it easy to select different combinations of equipment. This may take a few minutes, but once accomplished you dont need to do it again.
Even if you have a complex macro setup involving multiple flashes and extension tubes, it will provide a reasonable starting point for possible exposures at various fStops, speeds, and flash power settings.
PhotoCompute provides a full toolbox of photographic calculations that cant be fully listed within this site. Please go to the Web page to look at a fuller description of the app, and a lot of screenshots to get a sense of what else the app can do.