You can fix the time period for when your analysis begins by clicking on the button at the top of the LiveImpact table. This will turn the button orange to activate it and will fix the values in the 'before' column so that, regardless of how many changes you make to the scenario, they will always be compared to that specific point in time.

 

To turn off this feature, simply click on the button again so that it turns grey in colour.

 

You cannot select another potential while this is locked.