The Validation and Design to Cost tabs are designed for a very logical workflow: Start with the Validation tab so that you can understand and evaluate (and potentially adjust) some of the basic assumptions that aPriori has made when costing your part. You should also note if there are any Uncosted GCDs, so you can investigate this further. To investigate further, use the Issues pane on the Design to Cost tab or use the Messages pane to see how the GCD was processed. Then you can use the Design to Cost tab to understand and evaluate (and potentially adjust) the design-related cost driver details.