Let's take summing up to another level. Let's say you create a sub-sub table called "Auto Expenses" that is a child of your "Automobile" table. (See Designing Sub Tables for more on designing sub tables.) Imagine you would like to sum all the expenses for each Automobile and also sum ALL expenses for ALL Automobiles up to the Contact record. This can be easily accomplished by following the steps on Summing Up Parent Table
In this diagram we modified two columns to complete the overall function
The AMOUNT column in the Automobile Expense table is summed up to "Expense Total" field in the Automobile table.
Then the EXPENSE TOTAL column from the Automobile table is summed up to the "Expense(s) Total" field in the Contact table.