I don't understand... there isn't anything to calibrate.... its on the same scale as the rest of the graph. If its three lines up you are running at an instantaneous rate that would get you 30MPG.... etc. If you are on a flat level surface and can hold the instant bar at one point longer than a minute you'll see what I mean. Basically when the average graph to the right updates the green will be at the same height as the instantaneous bar was... so its on the same scale as far as I can tell.