From PDA Solutions 4U:
Fuel Trakker is a compact PDA program that has the ability to track fuel records for up to 15 vehicles. You have the capability to monitor records using the units of your choice. That is, liters versus gallons or Mpg versus km/L and many more. The option the convert existing database entries to different units is available too.
Fuel records can be entered in any order. There is a built in validation checker to verify data entries. For example, more recent entries must have higher odometer readings and vice versa. Unlike other programs that have you calculate the distance you traveled from the previous fuel purchase then enter the value into the program, Fuel Trakker handles all of the operations for you. You can even enter records out of order, just as long as the new entry meets Fuel Trakker's validation requirements.