This may be an over simplification, but I think Rich is alluding to it;
Let's say you are measuring back pressure on an installed tube, utilizing a
manometer. It seems to make sense that if the back pressure is correct for
the altitude, then the cfm should be correct also.
It should be possible though that you can reach a point where the tube
cannot pass anymore air, but the back pressure will increase.
73 Jay W7CW
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