The accounting method for a specific contract can be set by navigating to the "Advanced Settings" sub tab. From here, you can determine whether you want to use an "Amount Based" or "Unit/Quantity" based accounting method. An amount based accounting method allows you to enter a lump sum amount on a line item for your schedule of values. Inversely, the unit/quantity based accounting method allows you to input the quantity and unit price for a given item and the system auto calculates the total value of the line item for you.
Note: If you have one or more line items on the contract, you will not be able to change your accounting method.