To calculatete the cost of buying and owning one particular vehicle, click on the "Single Scenario Calculation" radio button, fill in the left-hand column with the vehicle data and then click the "Compute Costs" button. To compare buying and owning one vehicle with another, click on the "Double Scenario Calculation" radio button, fill in the both columns with each vehicle's data and then click the "Compute Purchase & Ownership Costs" button. If both vehicles have similar data, you can fill in the first column with the "Single Scenario Calculation" radio button selected, and then click on the "Copy Scenerio #1 to Scenario #2" button to fill in the right-hand column (be sure to switch to the "Double Scenario Calculation"). Then just change any cells that are different before computing.