"Average MPG" keeps resetting. Why?

I use "Trip 2" to track lifetime fuel economy, and it's doing so nicely. But I'd like to use "Trip 1" to track per-tank fuel economy. The trouble is "Trip 1" resets after the car has been shut down and the doors locked. (Don't know if Trip 2 would do that too if I had it active when I lock the car.)

Any way to get the car to stop resetting every time I lock the doors?

-mickey

"Average MPG" keeps resetting. Why?