Assumption preferences, set with Preferences, then Assumptions, are similar to those for forecasts, described in Setting Forecast Preferences. By default, assumption charts are not shown when you run a simulation. You can change the Show Automatically setting to automatically show assumption charts while a simulation is running or when it stops.
While the Forecast Preferences dialog has a button for fitting distributions to forecasts, distribution fitting isn’t available in the Assumption Preferences dialog. Instead, there is a Run Preferences button so you can easily change the Store Assumption Values... setting on the Options tab of the Run Preferences dialog. For more information on the Assumption Preferences dialog, click the Help button in the dialog.