[paulca]

Fuel used = Throttle position * RPM * time.

50% throttle at 1,500rpm will use half the fuel that 50% throttle at 3,000rpm will. (Assuming a linear map, which we don't really have). Maybe a little less, 1-2% less at 1,500rpm.

I use both the instant and average and I work on the principle of how much torque do I need. If I don't need torque to accelerate I shift for about 1,500rpm

Tonight on the way home I was at 30mph in a 30mph zone in 6th, circa 1,250rpm, maintaining speed and the instant MPG was reading 62mpg.

There is an agrument that says, 50% throttle at 1,500rpm to get X torque uses the same fuel as 25% throttle at 3,000rpm, but it doesn't. The higher the rpm the less efficient the engine. This is simply the physics of friction and momentum.

So if you are driving for fuel economy, low revs, high gears, plan ahead, avoid braking and be very gentle and smooth with the throttle.