Roger Head writes:

In those bazillions of specs the CFM is generally the displacement of
the pump, which we all know is a far cry from the amount of air that it
actually delivers.

That should always be called "displacement CFM", which is indeed a bogus
spec.

If a commercial product has a sticker claiming CFM at some psi, it had
better deliver that at the output fitting, unless otherwise set forth as
the theoretical displacement or some other nonsense. That the cheap
imports have misrepresented such standards of performance, doesn't nullify
the clear meaning of the specification.