From Surprise Software:
Adding new information becomes easier with every entry since Miles remembers many of the details of the entry. You'll fill out the form quickly by only entering new information. Most of the information can be selected from pre-populated lists of previously entered information. Entering the miles is easy also because you only need to enter two out of the three fields and the final field will be calculated. Do you know when you started and how many miles you traveled? Then the ending miles will be calculated. Do you know how many miles you went and what the ending odometer reading was? The starting miles will be calculated for you. If you know the starting and ending odometer readings, the trip can be calculated for you.