I've provided two methods as attached;
Sheet 1 involves creating a calculated field for each 'Scenario'. The downside is you need one calculated field per scenario. The upside is, you can control the placement of the metrics/columns better.
Sheet 2 is more dynamic and uses a table calculation to assess the difference from the scenario to the previous scenario. The upside is you create it once and you're done. The downside is, there's less control over where / how you show this difference, how you label it etc.
sample_tw.twbx 22.0 KB