2002 Regal GS - MPG indicator

I have come across a 2002 Regal GS for sale. I am interested in buying it but I have some concerns. The MPG indicator always reads 22 MPG. I drove it for about 3 miles. I expected to see some change. Is this 'gauge' real-time or if not, how often does it update?

Thanks,

Bill

Press the reset button while driving....mpg should go to zero, and then start recalculating mileage....This will be an average of the amount of time driving.....so naturally after a reset, it will dramatically change the average depending on the load on the engine(coasting will increase it, hard pedal will decrease it)......after being driven for a long period of time(weeks), whether you lay into it or coast, won't have much of an effect.....

22 is low, UNLESS it is because of a lot of local driving....