Computed gas mileage

[MJB3]

I think that this question is quite generic but I ask it here because of the expertise that I feel resides on this forum. I would like to know if the gas mileage, as computed on board, is developed using a moving average of say, the last 500 miles or is it computed from the last time it was reset. If one never reset it, would it indicate the mileage from the first day in service?

[WWWPerfA_ZN0W]

This is what the 2015 manual states:

 

Trip 1 and 2

Fuel Used — Shows the amount of fuel used for a given trip.
Average Fuel — Shows the average fuel economy for a given trip.

Fuel Economy

Inst Fuel Economy - Shows a visual graph of your instantaneous fuel economy along with your Avg MPG since the function was last reset.
Long Term Fuel Economy - Shows your long term fuel economy (I assume this is from the "beginning of time")

Fuel History - Shows a bar chart of your fuel history.
Average Fuel — Shows the average fuel economy for a given trip.
All Values — Shows all fuel economy values (DTE, Inst Fuel Econ, Avg Fuel).
Note: You can reset your average fuel economy by pressing and holding the OK button on the left hand steering wheel controls.

[MJB3]

Thanks for the reply. As you stated in regard to the Long Term Fuel Economy, "I assume this is from the "beginning of time"" leaves me with the same question. Is "Long Term" based on a rolling average, on the last 5 fill ups or some other undefined parameter? This is not of earth shaking importance, I was just wondering.