Adding data to the bottom of a list

[Jon_Hanes]

I am working on a spreadsheet that will help track mileage on certain vehicles. I would like to have a way to input information into a spreadsheet and allow the difference between last months mileage and this months mileage to show up on the bottom of the list. This is what I'm hoping it can look like.
Column A
----------------
Type of Car
Old Value
New Value
Difference for Jan
Difference for Feb
etc...


Then every time I enter a new value, the difference of these two numbers will keep going to the bottom of the list so that I can keep track of the number of miles used on that car each month. So what I will have at the end of the year will be the number of months used per month and a total number of miles used at the end of the year. At this point in time, I really don't care how it looks as long as it gets the results.

Please advise!
Jon